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AMN Construction · Trade secrets · Plumbing

Trade 06 of 13

Plumbing, hidden fast, so decide first.

Pipes disappear into walls quickly. Fixture choices have to be made before the walls close, because the pipes are set to fit them.

In short

  • Drains need slope and a vent. Without them, they gurgle, slow down or back up.
  • Pipe positions come from the fixture you picked, so pick fixtures first.
  • Plumbers come twice: once to run pipes in the walls, and again to set the fixtures at the end.
Drawing: Plumbing12345
  1. FixtureThe sink, toilet or tub. Its spec sheet sets where the pipes must stop.
  2. TrapA U-bend that holds a plug of water to block sewer gas.
  3. SlopeDrains fall about a quarter inch per foot so water carries waste away.
  4. VentLets air in behind the water so it drains smoothly and the trap stays full.
  5. To the sewerThe main drain leaves the house here.
A drain with a trap, a vent and a slope toward the stack. The trap holds a plug of water that blocks sewer gas, and the vent lets air in so water can drain.

What you will see

In the order it happens.

  • NoiseMedium
  • MessLight
  • Your sayHigh
  1. Step 1

    Pipes are run in the slab or walls, to fixtures that are not yet installed.

  2. Step 2

    The system is pressure tested and inspected before walls are closed.

  3. Step 3

    Months later, after tile, cabinets and paint, the plumber returns to set toilets, sinks and faucets.

  4. Step 4

    The water heater is started, and every fixture is run to check flow and drainage.

How it is done well

The techniques that matter.

  • Drain lines slope about a quarter inch per foot and every fixture is vented.
  • Supply pipes must hold pressure and drains must hold water, and the inspector sees both tests.
  • Shutoffs are accessible, and the water heater has room to be serviced.
  • Shower valves are set at the depth of the finished wall, tile included.

The hardest parts

Where this trade earns its fee.

  • Connecting to old drains, especially cast iron under existing slabs.
  • Bathrooms above living spaces, where noise and leaks matter most.
  • Long waits for hot water in big houses, which a recirculation line can fix.

Think deeply here

Decide this before the trade starts.

These are the choices that decide whether the finished house matches the one in your head. Changing them later costs time and money.

  • Exact fixture models, because their spec sheets set where the pipes go.
  • Shower design: heads, body sprays, a bench, a niche, curb or no curb.
  • Heat pump, tank or tankless water heater, and where it lives.
  • Gas lines for the range, fireplace, dryer or outdoor kitchen.

Ask any builder

  • Which fixtures are the pipes set for?
  • Where are the main and fixture shutoffs?
  • Is the water heater placed so it can be serviced and replaced?
Before thisWindows and exteriorNext on siteElectrical

All the trades, in the order you will meet them

  1. 01Site work
  2. 02Foundations
  3. 03Framing
  4. 04Roofing
  5. 05Windows and exterior
  6. 06Plumbing
  7. 07Electrical
  8. 08HVAC
  9. 09Insulation
  10. 10Drywall and plaster
  11. 11Tile
  12. 12Cabinetry
  13. 13Floors and paint

General guidance, not a specification. Your drawings, your engineer and your building inspector govern every job. See the whole process · Trade secrets home

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Updated October 2026

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