How to Add & Vent a Basement Toilet


Installing a basement toilet, or commode, increases your home’s value and reduces the line of family members waiting outside the main floor bathroom. Most homes have rough-in basement plumbing, so adding a toilet in the basement is a relatively simple home improvement task. Provisions for the sewer drain and the vent pipe are already in place. All you have to do is set the toilet and connect the vent to the existing plumbing.

Things You'll Need

  • Wax commode ring
  • Wrench
  • 2-inch PVC pipe
  • 2-inch PVC couplings
  • Pipe saw
  • PVC primer
  • PVC glue
  • Water supply line
  • 3/8-inch flexible water supply tubing
  • Drill (optional)
  • 1/2-inch hole drill bit (optional)
  • 3/8-inch PVC T-fitting (optional)

Setting the Toilet

  • Locate the toilet flange in the basement. This round cap lies flush with the surface of the concrete.

  • Remove the cap from the toilet flange and insert the two closet bolts, which came with the new commode, into the two slots on either side of the flange. The closet bolts will slide downward, then sideways, locking in place.

  • Position a new wax commode ring on the base of the toilet, pressing it down gently until it adheres well.

  • Set the commode carefully over the protruding ends of the closet bolts. The commode base features two holes, one on on either side. It helps to have at least two people set the commode -- one person to slowly lower it and the other to guide the bolts through the corresponding holes.

  • Place the nuts that came with the closet bolts over the tops of the bolts, and tighten them with a wrench just until they’re snug. Don’t over-tighten the nuts.

Venting the Toilet

  • Find the 2-inch PVC pipe that extends a foot or two out of the basement floor. This pipe serves as both the drainpipe for a sink/vanity and the vent for the basement bathroom, including the toilet. If you’re also installing a sink, use a sanitary T-fitting to connect the horizontal sink drain to the 2-inch vertical drain. If you’re not installing a sink, you’ll still use this pipe as a vent.

  • Locate the PVC pipe stub in the joist space directly above the 2-inch drainpipe. Remove the cap from the end of this stub. This is usually a screw-on cap, but if it’s glued on, cut it off with a pipe saw just above the cap.

  • Attach a PVC coupling to the top of the pipe that extends from the floor and attach another PVC coupling to the end of the pipe located in the joist space.

  • Measure the distance between the upper pipe stub and the lower pipe, and cut a section of 2-inch PVC pipe to match.

Hook Up the Water Supply

  • Connect the pipe to both the upper and lower couplings. Use PVC primer first, then apply PVC glue, as directed on the label of each product.

  • Install the toilet water supply. You can do this one of two ways. If the home has a manifold water distribution center, attach a flexible blue PEX tube to a new blue valve on the manifold and run the tube along the joists above until you reach the wall stud behind the toilet, and then bring it down.

  • Drill holes, if necessary, through wall studs or through the top wall plate with a drill fitted with a 1/2-inch hole bit. This is large enough for a 3/8-inch PEX tube.

  • Connect the water supply tube to an overhead water supply tube, if no manifold distribution center is available, by cutting the existing tube and installing a 3/8-inch T-fitting.

  • Attach the tube to the water supply hose on the toilet. The hose will have a valve that allows you to turn off the water to the toilet. The outlet on the other side probably has a compression fitting. Slip the end of the tube over the fitting and turn the attached nut to hold the tube in place.

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