How to Add a Toilet to a Sewer Stack in a Basement

Basement toilets typically connect to roughed-in plumbing beneath the concrete floor.

The sewer stack, also called the vent-and-soil stack, is the main waste and water drainage system, featuring a 4-inch pipe that flows into to a horizontal main sewer line. The vertical pipe runs to the top of the house, exiting through the roof. Starting in the 1970s, most communities adopted building codes requiring basement plumbing rough-ins, called “stubs.” When you install a toilet in the designated spot, it will automatically be added to the sewer stack. You’ll have to install a sink or install a vent pipe where the sink would be, to provide the necessary vent for the toilet.

Things You'll Need

• Two water closet bolt sets
• Wax commode ring
• 2-inch sanitary T-fitting
• 2-inch PVC pipe
• 2-inch PVC coupling
• Pipe saw
• PVC glue
• PVC primer

Instructions

1. Locate a 4-inch round cap set in the concrete basement floor. Beneath the cap lies the toilet flange. Nearby, you will find a 2-inch pipe that extends about 2 feet out of the concrete and a square in the floor that's filled with sand or soil.

2. Remove the toilet flange cap and insert a long water closet bolt on both sides of the flange. Two small slits accommodate the bolts. Insert at bolt by putting the narrow end into the side of one slit and then pushing it to the other side to lock it in place. Do the same on the other side of the flange.

3. Fit a wax commode ring on the base of the toilet or over the flange.

4. Set the toilet by lowering it over the tops of the water closet bolts. The toilet has one hole in the base on both sides to accept a bolt.

5. Slip a washer and a nut on each bolt and tighten the nuts with a wrench until they’re snug but not overly tight. The washers, nuts and bolts all come in the water closet bolt set.

6. Install a vanity sink and connect a 2-inch sanitary T-fitting between the sink drain and the 2-inch drain stub that extends out of the floor. When you attach any type of PVC pipes or fittings, apply PVC primer first to prep the areas that fit together and then apply PVC glue as directed by the glue manufacturer.

7. Add a 2-inch PVC pipe to the top of the sanitary T-fitting, connecting it to the pipe stub between the ceiling joists directly above the pipe. This is the vent for the entire bathroom group, including the toilet.

Tips & Warnings

• If you don’t want to install a sink, you still have to connect the pipe for the sink drain to the stub between the ceiling joists. To do this, install a PVC coupling, instead of a sanitary T-fitting at the bottom, run the pipe and use a coupling at the top to connect the pipe to the upper vent stub.

• If the house is older and does not have roughed-in plumbing, you can install an up-flush toilet, featuring a tank that grinds and pumps macerated waste into the main sewer line. An up-flush toilet also has a connection on top of the tank for a vent pipe.

• The shower or tub drain connects to a buried drainpipe in the sand-filled square on the basement floor.