In this video, This Old House plumbing and heating expert Richard Trethewey shows how to rough-in the drainpipes for a basement bathroom.
- Lay out the 2×4 bottom wall plates to establish the perimeter of the bathroom walls.
- Measure off the wall plates to locate the center of the shower drain and toilet flange.
- Dig a trench extending from the existing drainpipe over to the new locations of the shower drain and toilet flange.
- Use a right-angle grinder fitted with a diamond-impregnated cutting wheel to cut through the old cast-iron drainpipe.
- Attach a flexible no-hub mechanical coupling onto the end of the just-cut drainpipe. Tighten hose clamp onto the cast-iron pipe with a torque wrench.
- Cut and glue together 3-inch-diameter PVC pipes and fittings to form the drainpipe assembly that connects the old cast-iron pipe to the new shower and toilet drain.
- Slip the end of the PVC drainpipe assembly into the mechanical coupling attached to the old cast-iron pipe. Tighten the hose clamp to secure the PVC pipe.
- Next, run 2-inch-diameter PVC pipe from the drainpipe assembly over to the shower and vanity sink.
- Install traps for each fixture, and be sure the pipes slope ⅛ inch per foot to drain properly.
- Drive a ½-inch-diameter steel-reinforcing bar down into the soil beside each trap. Then, use duct tape to secure the bars to the traps.
- Have the rough piping inspected before pouring the concrete floor.
- Cover the open end of the toilet pipe with a foam cap. Wrap plastic around the shower-drain pipe.
- Have the concrete contractor pour a new floor around the piping.