Basement Bathroom Plumbing Installation


Discover the main steps of installing basement bathroom as a DIY project if you are a real pro.

Supply line plumbing

  • Locate the main drain run. (look for a 3- or 4-inch main “stack” coming down one of the walls).
  • Find a sewer clean-out fitting by the wall facing the street or driveway.
  • Mark the floor to show the drain run and where you want to do your shower installation, toilet and sink drains.
  • Break the concrete along the main drain with a sledgehammer.
  • Dig an exploratory hole (2 to 3 feet across) or two where you assume tying in new plumbing to the main drain.
  • Verify the planned bathroom plumbing installation.
  • Make necessary changes to the layout, and clearly mark the floor with the locations of new drains.
  • The pipe runs should have a slope of ¼ inch per foot (or ⅛ inch per foot according to local codes).
  • Make sure the longest run of the drain has a sufficient height above the main for the run.

Basement bathroom plumbing installation

  • Break out the concrete for the new bathroom drains. The shower needs added depth to accommodate a trap, both the toilet and sink have their own traps. Determine how to run the vent pipes.
  • Remember, every drain has a vent pipe and code. Any pipe under a slab has to be 2 inches (except the toilet drain, which must be 3 inches or larger).
  • After digging assemble the pipe. Do not glue anything.
  • Break into the cast iron drain to assemble the Y-fitting with a pipe snapper.
  • Use a hacksaw if you work with old crushing cast iron
  • Cut out the appropriate length to accommodate the no-hub Y-fitting
  • Assemble the drain system. Make sure the downward slope, and the vertical location of the drains are correct.
  • Inspect the new drain system. Get the approval of the building inspector before filling the drain trench.
  • Fill in the holes to 3 inches below the floor. Pour 3 inches of concrete to replace, and level the floor.

Installing basement bathroom

  • Frame the bathroom.
  • Run the vent pipes from each drain.
  • Do not concrete the area surrounding the shower drain. Leave it open if you need to reposition the drain when the shower pan is framed in.
  • If the drain is correct, finish the concrete.

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