Things You'll Need
Soil pipe, 4-inch PVC
Drain pipe, 3-inch PVC
A closet bend is the 90-degree angle pipe installed beneath your toilet in the bathroom. This is the most important and often challenging part of toilet plumbing, but if you know what to do, it is very manageable. The closet bend attaches to two different pipes including the soil pipe, a drain pipe directly below the toilet that connects directly to the toilet flange, and the drain stack, the major drain line in your home. To install it correctly, dry fit the pipes first before bonding them permanently.
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Install a section of 4-inch PVC soil pipe on the top opening of the closet bend -- the opening nearest the toilet. Slide a 4-by-3 toilet flange onto the top of the soil pipe. Adjust or cut the pipes so the flange is perfectly level with the floor and the closet bend is suspended just below the flooring in the joists. Mark the pipes with a marker at each seam as a guide.
Disassemble the pipe, coat the ends of the soil pipe and closet bend with PVC pipe primer and then again with PVC cement. Push the soil pipe into the closet bend up to the mark you made previously.
Coat the end of the flange and top of the closet bend with PVC primer and cement. Push the flange onto the closet bend from above the floor. Make sure the flange is level with the floor.
Screw the flange mounting collar to the floor with galvanized or rust-proof screws.
Route pipes to the main drain stack from the outlet end of the closet bend. Measure the length to the main drain stack with a tape measure, cut and install 3-inch PVC drain pipe from the closet bend back to the main drain stack at a slope of 1/8 inch per foot. Dry fit all the pipes together.
Disassemble the pipes, coat the ends of each with PVC primer and cement and push the pipes back together and let them dry.