What size pipe for toilet drain?
The wider the pipe, the more waste it can move and the less likely it will be to clog. A 4-inch pipe for a toilet is recommended and can carry about twice the waste of a 3-inch drain. The toilet flange is the fitting that attaches the toilet to the drain line. Flanges are available in a variety of configurations to allow the toilet and drain to attach securely. The diameter of the waste outlet for the toilet may not match the drain pipe.