KY Plumber cheat sheet

Kentucky plumbing work is governed by KRS Chapter 318 and 815 KAR Chapter 20; local governments may adopt stricter ordinances but may not adopt standards less stringent than the state code.

A master plumber license authorizes the licensee to contract for plumbing work and to employ journeymen and apprentices; a journeyman license authorizes work under a master's supervision but not contracting.

Apprentices must be registered with the state plumbing program and work under direct supervision; apprentice hours are documented and verified before journeyman examination eligibility.

A permit must be obtained from the local administrative authority before beginning installation, alteration, or replacement of plumbing, except for minor repair work specifically exempted by regulation.

Inspections are requested by the permit holder at defined stages: rough-in (before concealment), water and drainage testing, and final. Concealed work installed without rough-in approval is subject to removal.

A plumbing contractor must carry the state-required liability insurance and must display the license number on vehicles, contracts, and advertisements as required by 815 KAR 20.

Violations may result in fines, license suspension or revocation, and stop-work orders; unlicensed contracting is a separate violation chargeable against both the contractor and the property owner who knowingly hires.

Plans and specifications for certain occupancies (assembly, health care, large multi-family) must be submitted to the state plumbing program for review before a local permit is issued.

Plumbing is the practice, materials, and fixtures used in installing, maintaining, and altering piping, fixtures, appliances, and appurtenances in connection with sanitary drainage, venting, and water supply.

Potable water is water free of impurities in amounts sufficient to cause disease or harmful physiological effects, conforming to the primary and secondary drinking water regulations.

A fixture is a receptacle that receives water or waste and discharges it to the drainage system; a fixture fitting is a device that controls or directs the flow from a fixture to the drainage system.

Cast iron soil pipe is available as service (hubless, no-hub) weight and extra-heavy weight; no-hub couplings must be listed and the clamp torque specified by the manufacturer.

PVC and ABS DWV pipe are joined by solvent cement; the cement and primer must be listed for the specific material, and ABS and PVC may not be joined to each other with solvent cement.

Type L copper is standard for domestic water; Type M is permitted only where allowed by code and not for underground or concealed installations where prohibited by local amendment.

PEX tubing must be listed to ASTM F876/F877 and fittings to F1807 or F1960; PEX shall not be installed within the first 18 inches of the outlet of a water heater unless the manufacturer approves.

Every material, device, and appurtenance must be listed by an approved testing agency (e.g., CSA, UL, NSF) and installed per the manufacturer's instructions and the referenced standard.

A drainage system is sized by drainage fixture units (dfu); the building drain and sewer are sized from the total dfu using the code's slope-dependent sizing tables.

Horizontal drainage pipe must be installed at a uniform slope of not less than 1/4 inch per foot for pipe 2 1/2 inches and smaller, and not less than 1/8 inch per foot for 3-inch and larger pipe.

No horizontal drainage pipe may be installed at a slope greater than 1/2 inch per foot unless it is a vertical drop or an approved steep-slope arrangement.

Changes in direction of drainage pipe: 2-inch and smaller may use short-radius fittings; 3-inch and larger must use long-sweep fittings or two 45-degree fittings for horizontal-to-horizontal changes.

A building drain is the lowest pipe receiving soil and waste inside the building; it extends 30 inches outside the building wall and becomes the building sewer at that point.

Cleanouts are required at the base of each vertical stack, at the building drain, at the junction of the building drain and building sewer, and at intervals not exceeding 100 feet in horizontal runs.

A backwater valve is required on fixtures whose drainage outlets are below the level of the next upstream manhole, to prevent sewage backup into the building.

Drainage pipe passing under a footing or wall must be protected by relieving arches or sleeves providing at least 2 inches of clearance on all sides.

Water closets must be of the low-consumption type, using no more than 1.6 gallons per flush; urinals are limited to 1.0 gallon per flush.

A fixture trap must have a liquid seal of not less than 2 inches and not more than 4 inches, and the trap seal depth is measured from the crown weir to the top of the dip.

Each fixture must be individually trapped, except that a single trap may serve a set of not more than three lavatories or sinks that are in the same room and share a common waste.

The developed length of a fixture trap arm from the trap weir to the vent fitting may not exceed the values in the code table (e.g., 3 1/2 feet for 1 1/4-inch and 5 feet for 1 1/2-inch pipe).

A fixture trap must be self-cleaning; bell traps, S-traps, and drum traps are prohibited except for specific approved uses such as interceptors or where a drum trap is permitted by the authority.

Floor drains must be provided with a trap and, where subject to evaporation, a trap primer or a trap seal protection device to maintain the required 2-inch minimum seal.

Fixture clearances: water closets require at least 15 inches center-to-sidewall and 21 inches in front of the bowl; lavatories require at least 4 inches of clearance from a sidewall to the bowl.

A fixture shall not be set closer than 2 inches to a wall or partition unless the fixture is designed for that installation, and every fixture must be accessible for cleaning and repair.

A temperature and pressure (T&P) relief valve is required on every water heater; the valve must be set to open at or below the tank's rated working pressure and at a temperature not exceeding 210 degrees F.

The T&P relief valve discharge pipe must be full-size, gravity-drained, terminate not more than 6 inches above the floor or outside the building, and must not be trapped, reduced, or threaded at the end.

A thermal expansion tank is required on a closed domestic water system to control pressure caused by thermal expansion of water during heating.

Water heaters installed in a garage must be elevated so the ignition source is at least 18 inches above the floor, or be of the flammable-vapor-ignition-resistant type.

A water heater must be provided with a shutoff valve on the cold water inlet and a means to drain the tank; the drain valve outlet must be accessible.

Seismic or restraint straps are required where the authority having jurisdiction determines they are necessary; in Kentucky, strapping is typically required for tanks over 30 gallons in certain occupancies.

Scald protection: shower and bathtub/shower valves must be of the pressure-balancing or thermostatic mixing type, and the maximum delivered temperature at a shower is limited to 120 degrees F.

Water heaters installed in a confined space must have combustion air openings sized per the fuel gas code; two openings, each sized at 1 square inch per 1,000 Btu/h input, are required for direct-vented appliances.

Water supply pipe is sized using the water supply fixture unit (wsfu) method; the total wsfu and the developed length are used to select the pipe size from the code table.

Minimum residual pressure at a fixture is 8 psi for flush valves and 15 psi for fixtures with a tank-type flush, measured at the fixture outlet.

The minimum size of a building water service is 3/4 inch; the minimum size of a fixture supply is 3/8 inch.

A water service must be protected against backflow by an approved device; a reduced pressure principle backflow preventer is required for high-hazard connections such as irrigation, boilers, and chemical systems.

A main shutoff valve must be installed on the water service near the point of entry, and a full-open valve must be provided on each fixture supply.

Water distribution pipe must be protected from freezing; in Kentucky, the frost depth is generally 30 inches, so buried service lines must be below that depth or otherwise protected.

A water hammer arrestor is required where quick-closing valves are installed, such as at flush valves and solenoid-operated appliances, to control pressure surges.

Hot water distribution: the developed length from the water heater to the farthest fixture should not exceed 100 feet; recirculation is required where the length exceeds the code limit.

Every fixture trap must be protected by a vent; the vent must be installed on the outlet side of the trap and within the trap arm length limit.

A vent stack must extend at least 6 inches above the roof and at least 3 feet above any roof surface within 10 feet, and must not terminate within 10 feet of an operable window or air intake.

The vent stack size is determined by the total vent units it serves; a vent stack serving a building drain must be at least 1 1/4 inches in diameter and not smaller than the drain it serves.

A common vent may serve two fixtures on the same floor where they are within 2 inches of the same size and the common vent is at least 1 1/2 inches in diameter.

A wet vent is a vent that also serves as a drain for fixtures on the same floor; the wet vent must be at least 2 inches in diameter and may serve only fixtures in the same bathroom group.

An island sink must be vented by either an island vent (loop vent) or an air admittance valve installed per the manufacturer's instructions and the code.

A stack vent is the extension of a soil or waste stack above the highest horizontal drain; it must be at least the size of the stack and extend above the roof.

Vent pipe must be installed with a slope of not less than 1/4 inch per foot toward the drain and must be protected against frost closure by increasing the size to at least 3 inches where required.

A grease interceptor is required for commercial kitchens, restaurants, and other establishments where grease-laden waste is discharged; it must be sized per the code based on fixture capacity and flow rate.

A grease interceptor must be installed outside the building unless an indoor unit is specifically approved, and it must be accessible for cleaning and inspection.

A sand and oil interceptor is required for automotive repair, service stations, and similar occupancies where oil, sand, or similar waste is discharged.

An interceptor must be vented to prevent the development of a vacuum or back pressure; the vent must be installed on the outlet side of the interceptor.

A trap seal primer is required for traps serving floor drains, floor sinks, and similar fixtures subject to evaporation; the primer must deliver water to maintain the trap seal.

A backwater valve is a device that prevents the reversal of flow in a drainage system; it must be installed on the building drain or sewer and be accessible for inspection.

An air admittance valve (AAV) may be used to vent a fixture trap where permitted by the code; it must be installed in an accessible location and in accordance with the manufacturer's instructions.

Interceptors and separators must be sized and installed per the manufacturer's instructions and the referenced standard, and the accumulated waste must be removed at the required interval.

Storm drainage is sized using the roof area and the local rainfall intensity; the roof area is the projected horizontal area of the roof plus the area of any vertical walls that drain to the roof.

The rainfall intensity used for sizing is the 100-year, 1-hour rainfall rate for the locality; for Kentucky, values are typically in the range of 2.5 to 3.5 inches per hour.

Roof drains must be installed with a strainer and a sump; the leader or conductor must be sized from the roof area and rainfall intensity using the code table.

A secondary (emergency) roof drain or scupper is required where the primary roof drain could become blocked; the secondary drain must discharge to a location where overflow will not cause damage.

Storm drainage may not connect to the sanitary drainage system; the two systems must be separate and independently vented.

A sump pump or ejector is required to lift drainage from a point below the gravity drain; it must be provided with a check valve and a vent.

Special plumbing systems include acid waste, chemical waste, and laboratory drainage; these must use materials resistant to the waste and be vented per the code.

A trap primer is required for floor drains in parking garages, mechanical rooms, and other areas where the trap seal may evaporate.

Health care facilities require plumbing fixtures and piping that resist corrosion and are easily cleaned; fixtures must be of the floor-mounted or wall-mounted type with smooth, nonabsorbent surfaces.

A clinical sink (bedpan washer) must be provided with a trap and a flushing rim, and must be installed with a backflow preventer on the water supply.

Handwashing sinks in patient care areas must be located in each patient room or in an adjacent room, and must be provided with a soap dispenser and a towel dispenser.

A hose bibb or other connection with a potential for backflow in a health care facility must be protected by a vacuum breaker or a reduced pressure principle backflow preventer.

Medical gas and vacuum piping must be installed per NFPA 99 and the manufacturer's instructions; only licensed medical gas installers may perform the work.

Sterilizers, dialysis equipment, and other medical equipment must be connected to the drainage system through an air gap or an approved backflow preventer.

A floor drain is required in each patient bathroom, mechanical room, and other locations where water may accumulate; the drain must be provided with a trap primer.

Emergency eyewash and shower stations must be provided in areas where corrosive materials are used, and must be connected to the potable water supply with a backflow preventer.

The Kentucky Plumbing Code references the International Plumbing Code (IPC) as the model code, along with the International Fuel Gas Code (IFGC) for fuel gas piping.

Fuel gas piping must be installed per the IFGC and the manufacturer's instructions; the pipe must be sized using the longest length method or the branch length method.

Gas pipe must be supported at intervals not exceeding 6 feet for horizontal runs and at each change of direction; it must be protected against corrosion and physical damage.

A shutoff valve must be installed on each gas appliance connector and at the point where the gas piping enters the building.

Gas piping must be tested at a pressure of not less than 1 1/2 times the working pressure, but not less than 3 psi for a 10-minute test, or per the code's specified test pressure.

A sediment trap must be installed on the gas supply line to each appliance, downstream of the shutoff valve, unless the appliance is designed to prevent the accumulation of sediment.

Combustion air for fuel gas appliances must be provided per the IFGC; a confined space requires two permanent openings, each sized at 1 square inch per 1,000 Btu/h input.

A gas appliance connector must be listed, not exceed 6 feet in length, and must not be concealed or pass through a wall, floor, or ceiling.

Drainage fixture units (dfu) are assigned by fixture type: a water closet is 3 dfu, a lavatory is 1 dfu, a bathtub is 2 dfu, a kitchen sink is 2 dfu, and a floor drain is 1 dfu (per the code table).

Water supply fixture units (wsfu) are assigned by fixture type and by whether the fixture is a flush valve or a tank type; a water closet with a flush valve is 10 wsfu and with a tank is 2.5 wsfu.

Developed length is the total length of pipe measured along the centerline of the pipe and fittings, including the equivalent length of fittings; it is used to size water supply pipe.

The equivalent length of a fitting is expressed in feet of pipe and is added to the actual pipe length to obtain the developed length; a 90-degree elbow is typically equivalent to 2 to 3 feet of pipe.

Slope is expressed as a ratio of vertical drop to horizontal run; a 1/4 inch per foot slope is a 2 percent slope, and a 1/8 inch per foot slope is a 1 percent slope.

To convert slope to a percentage, divide the drop by the run and multiply by 100; a 1/4 inch per foot slope equals 0.25 divided by 12 times 100, or 2.08 percent.

An isometric drawing shows the plumbing system in three dimensions; the isometric is used to interpret the layout of drainage, vent, and water supply piping and to determine pipe lengths and fittings.

When interpreting an isometric, vertical lines represent vertical pipe, and lines drawn at 30 degrees to the horizontal represent horizontal pipe running in two directions.

A soil pipe carries sewage containing fecal matter; a waste pipe carries liquid waste free of fecal matter; a drain carries waste from fixtures to the building drain.

A stack is a vertical pipe that carries waste or soil; a vent stack is a vertical pipe that provides venting for a drainage system.

A building sewer is the pipe that carries sewage from the building drain to the public sewer or private disposal system; it begins 30 inches outside the building wall.

A fixture unit is a measure of the load-producing effect of a fixture on the drainage or water supply system; it is used in sizing calculations.

A trap seal is the water in a trap that prevents the passage of sewer gas; it must be at least 2 inches and not more than 4 inches deep.

A vent is a pipe that provides a flow of air to or from a drainage system to protect trap seals; a vent may be a stack, a branch, or a loop.

A cleanout is an access opening with a removable plug or cover that provides access to a drain for cleaning; it must be gas-tight and accessible.

An air gap is the unobstructed vertical distance through the free atmosphere between the lowest opening of a water supply outlet and the flood level rim of a fixture; it must be at least twice the diameter of the outlet and not less than 1 inch.

The building drain must be sized to carry the total drainage load; a 3-inch building drain is limited to 20 dfu at 1/4 inch per foot slope, and a 4-inch drain is limited to 160 dfu at the same slope.

A vertical stack of 2-inch diameter may carry a maximum of 24 dfu; a 3-inch stack may carry 48 dfu, and a 4-inch stack may carry 120 dfu (per the code table).

A horizontal branch of 2-inch diameter may carry a maximum of 6 dfu; a 3-inch branch may carry 20 dfu, and a 4-inch branch may carry 160 dfu.

A cleanout must be provided at the base of each stack and at the building drain; the cleanout must be the same size as the pipe it serves and must be accessible.

A backwater valve must be installed on the building drain where the building drain is below the level of the next upstream manhole; it must be accessible for inspection and repair.

A drain passing under a wall or footing must be protected by a relieving arch or sleeve; the sleeve must provide at least 2 inches of clearance on all sides.

A horizontal drain must be supported at intervals not exceeding 4 feet for pipe 2 inches and smaller, and not exceeding 10 feet for pipe larger than 2 inches.

A vertical stack must be supported at its base and at each floor level; the support must be capable of carrying the weight of the pipe and its contents.

A water closet must be set level and securely fastened to the floor; the closet flange must be installed at the finished floor level and must be fastened to the floor.

A lavatory must be provided with a trap and a water supply; the lavatory must be set at a height of not less than 29 inches and not more than 36 inches above the floor.

A bathtub must be provided with a trap and a water supply; the bathtub must be set level and must be accessible for cleaning.

A shower must be provided with a trap, a water supply, and a shower valve; the shower floor must be sloped to drain at not less than 1/4 inch per foot.

A floor drain must be provided with a trap and a strainer; the strainer must be removable for cleaning and must have a free area of not less than the cross-sectional area of the drain.

A fixture trap must be installed level and must be accessible for cleaning; the trap must be provided with a cleanout plug or a removable trap.

A fixture fitting must be listed and installed per the manufacturer's instructions; the fitting must be of a type that does not obstruct the flow of waste.

A fixture must be provided with a water supply of sufficient volume and pressure to operate it; the minimum pressure at the fixture is 8 psi for flush valves and 15 psi for tank-type fixtures.

A water heater must be installed in a location where it is accessible for inspection and repair; it must not be installed in a closet unless the closet is provided with combustion air.

A water heater must be provided with a T&P relief valve; the valve must be installed on the tank and must be piped to a safe discharge location.

A water heater must be provided with a drain pan where the tank is installed in a location where leakage could cause damage; the pan must be piped to a safe discharge location.

A water heater must be provided with a shutoff valve on the cold water inlet; the valve must be accessible and must be of a type that can be closed quickly.

A water heater must be provided with a means to drain the tank; the drain valve must be installed at the lowest point of the tank and must be accessible.

A water heater installed in a garage must be elevated so the ignition source is at least 18 inches above the floor, or be of the flammable-vapor-ignition-resistant type.

A water heater must be provided with a temperature control; the maximum temperature at a shower is limited to 120 degrees F, and the maximum temperature at a bathtub is limited to 120 degrees F.

A water heater must be provided with a vacuum relief valve where the tank is installed with a bottom inlet; the valve must be installed on the cold water inlet.

The water service must be sized to provide the required flow and pressure; the minimum size of a water service is 3/4 inch, and the minimum size of a fixture supply is 3/8 inch.

The water distribution system must be sized using the wsfu method; the total wsfu and the developed length are used to select the pipe size.

The minimum residual pressure at a fixture is 8 psi for flush valves and 15 psi for tank-type fixtures; the pressure must be measured at the fixture outlet.

A water service must be protected against backflow by an approved device; a reduced pressure principle backflow preventer is required for high-hazard connections.

A main shutoff valve must be installed on the water service near the point of entry; a full-open valve must be provided on each fixture supply.

Water distribution pipe must be protected from freezing; in Kentucky, the frost depth is generally 30 inches, so buried service lines must be below that depth.

A water hammer arrestor must be installed where quick-closing valves are installed; the arrestor must be installed near the valve and must be accessible.

Hot water distribution must be insulated where required; the developed length from the water heater to the farthest fixture should not exceed 100 feet, and recirculation is required where the length exceeds the code limit.

Every fixture trap must be protected by a vent; the vent must be installed on the outlet side of the trap and within the trap arm length limit.

A vent stack must extend at least 6 inches above the roof and at least 3 feet above any roof surface within 10 feet; it must not terminate within 10 feet of an operable window or air intake.

The vent stack size is determined by the total vent units it serves; a vent stack serving a building drain must be at least 1 1/4 inches in diameter and not smaller than the drain it serves.

A common vent may serve two fixtures on the same floor where they are within 2 inches of the same size and the common vent is at least 1 1/2 inches in diameter.

A wet vent is a vent that also serves as a drain for fixtures on the same floor; the wet vent must be at least 2 inches in diameter and may serve only fixtures in the same bathroom group.

An island sink must be vented by either an island vent (loop vent) or an air admittance valve installed per the manufacturer's instructions and the code.

A stack vent is the extension of a soil or waste stack above the highest horizontal drain; it must be at least the size of the stack and extend above the roof.

Vent pipe must be installed with a slope of not less than 1/4 inch per foot toward the drain and must be protected against frost closure by increasing the size to at least 3 inches where required.

A grease interceptor must be installed for commercial kitchens and restaurants; it must be sized per the code based on fixture capacity and flow rate.

A grease interceptor must be installed outside the building unless an indoor unit is specifically approved; it must be accessible for cleaning and inspection.

A sand and oil interceptor must be installed for automotive repair, service stations, and similar occupancies where oil, sand, or similar waste is discharged.

An interceptor must be vented to prevent the development of a vacuum or back pressure; the vent must be installed on the outlet side of the interceptor.

A trap seal primer must be installed for traps serving floor drains, floor sinks, and similar fixtures subject to evaporation; the primer must deliver water to maintain the trap seal.

A backwater valve must be installed on the building drain or sewer and must be accessible for inspection; it must be a type that closes automatically when flow reverses.

An air admittance valve may be used to vent a fixture trap where permitted by the code; it must be installed in an accessible location and in accordance with the manufacturer's instructions.

Interceptors and separators must be sized and installed per the manufacturer's instructions and the referenced standard; the accumulated waste must be removed at the required interval.

Storm drainage must be sized using the roof area and the local rainfall intensity; the roof area is the projected horizontal area of the roof plus the area of any vertical walls that drain to the roof.

The rainfall intensity used for sizing is the 100-year, 1-hour rainfall rate for the locality; for Kentucky, values are typically in the range of 2.5 to 3.5 inches per hour.

Roof drains must be installed with a strainer and a sump; the leader or conductor must be sized from the roof area and rainfall intensity using the code table.

A secondary roof drain or scupper must be installed where the primary roof drain could become blocked; the secondary drain must discharge to a location where overflow will not cause damage.

Storm drainage may not connect to the sanitary drainage system; the two systems must be separate and independently vented.

A sump pump or ejector must be installed to lift drainage from a point below the gravity drain; it must be provided with a check valve and a vent.

Special plumbing systems include acid waste, chemical waste, and laboratory drainage; these must use materials resistant to the waste and be vented per the code.

A trap primer must be installed for floor drains in parking garages, mechanical rooms, and other areas where the trap seal may evaporate.

Health care facilities require plumbing fixtures and piping that resist corrosion and are easily cleaned; fixtures must be of the floor-mounted or wall-mounted type with smooth, nonabsorbent surfaces.

A clinical sink must be provided with a trap and a flushing rim; it must be installed with a backflow preventer on the water supply.

Handwashing sinks in patient care areas must be located in each patient room or in an adjacent room; they must be provided with a soap dispenser and a towel dispenser.

A hose bibb or other connection with a potential for backflow in a health care facility must be protected by a vacuum breaker or a reduced pressure principle backflow preventer.

Medical gas and vacuum piping must be installed per NFPA 99 and the manufacturer's instructions; only licensed medical gas installers may perform the work.

Sterilizers, dialysis equipment, and other medical equipment must be connected to the drainage system through an air gap or an approved backflow preventer.

A floor drain must be installed in each patient bathroom, mechanical room, and other locations where water may accumulate; the drain must be provided with a trap primer.

Emergency eyewash and shower stations must be installed in areas where corrosive materials are used; they must be connected to the potable water supply with a backflow preventer.

The Kentucky Plumbing Code references the International Plumbing Code as the model code, along with the International Fuel Gas Code for fuel gas piping.

Fuel gas piping must be installed per the IFGC and the manufacturer's instructions; the pipe must be sized using the longest length method or the branch length method.

Gas pipe must be supported at intervals not exceeding 6 feet for horizontal runs and at each change of direction; it must be protected against corrosion and physical damage.

A shutoff valve must be installed on each gas appliance connector and at the point where the gas piping enters the building.

Gas piping must be tested at a pressure of not less than 1 1/2 times the working pressure, but not less than 3 psi for a 10-minute test, or per the code's specified test pressure.

A sediment trap must be installed on the gas supply line to each appliance, downstream of the shutoff valve, unless the appliance is designed to prevent the accumulation of sediment.

Combustion air for fuel gas appliances must be provided per the IFGC; a confined space requires two permanent openings, each sized at 1 square inch per 1,000 Btu/h input.

A gas appliance connector must be listed, not exceed 6 feet in length, and must not be concealed or pass through a wall, floor, or ceiling.

Drainage fixture units are assigned by fixture type: a water closet is 3 dfu, a lavatory is 1 dfu, a bathtub is 2 dfu, a kitchen sink is 2 dfu, and a floor drain is 1 dfu.

Water supply fixture units are assigned by fixture type and by whether the fixture is a flush valve or a tank type; a water closet with a flush valve is 10 wsfu and with a tank is 2.5 wsfu.

Developed length is the total length of pipe measured along the centerline of the pipe and fittings, including the equivalent length of fittings; it is used to size water supply pipe.

The equivalent length of a fitting is expressed in feet of pipe and is added to the actual pipe length to obtain the developed length; a 90-degree elbow is typically equivalent to 2 to 3 feet of pipe.

Slope is expressed as a ratio of vertical drop to horizontal run; a 1/4 inch per foot slope is a 2 percent slope, and a 1/8 inch per foot slope is a 1 percent slope.

To convert slope to a percentage, divide the drop by the run and multiply by 100; a 1/4 inch per foot slope equals 0.25 divided by 12 times 100, or 2.08 percent.

An isometric drawing shows the plumbing system in three dimensions; the isometric is used to interpret the layout of drainage, vent, and water supply piping and to determine pipe lengths and fittings.

When interpreting an isometric, vertical lines represent vertical pipe, and lines drawn at 30 degrees to the horizontal represent horizontal pipe running in two directions.