Pipe Materials, Sizing, and Joining Methods
Match material to service
Copper tube comes in K, L, and M with decreasing wall thickness; L is the common plumbing choice, K for buried and heavy-duty service, M for some interior work per local amendment. PEX (A, B, C) is joined by expansion, crimp, or clamp depending on the system. CPVC and PVC are chemically different and need their own cement. PVC comes in pressure-rated schedules and DWV-only versions; ABS is a separate solvent-welded system. Cast iron, galvanized steel, and coated steel serve drainage and specialty services. Potable water materials must comply with lead-free requirements - no more than 0.25% weighted average lead in wetted surfaces.
Sizing logic
Sizing is a chain: fixture units and demand first, then velocity and friction loss, then developed length, then the code table. Confirm the material's pressure rating and temperature derating. Do not undersize a branch because "the fixture is small" - minimum branch sizes apply.
Joining
Solder and brazing require clean, fluxed surfaces and correct filler metal; press and push fittings follow the tool manufacturer. Solvent cement cure time depends on pipe diameter, ambient temperature, and the cement's own table - cold weather dramatically increases cure time. Threaded joints use approved tape or dope on male threads only. Dissimilar metals need a dielectric union or approved isolation to prevent galvanic corrosion. Grooved and flanged couplings have their own gasket and torque requirements.
Traps in questions
Using DWV PVC for pressure service; using PVC cement on CPVC; ignoring temperature derating of plastic pipe; direct copper-to-steel contact; and forgetting that solvent-cemented joints must cure before pressure testing.
Rule of thumb
When the question names a service (hot water, buried, gas, DWV), the correct answer is the material and joining method listed for that service - not the cheapest or most familiar material.