What Are the Guidelines for Drainage for Toilets?

The Trap

• All fixtures, including sinks, tubs and toilets, have a trap as part of their drain lines. The trap is a curved pipe that allows water to stay inside it after waste water and other materials drain through it. You can spot the trap most easily underneath a kitchen or lavatory sink, but on a toilet, the trap is actually built inside the bottom portion of the bowl. Often buyers look for toilets with trap ways that are slightly larger than other models and glazed to allow for easier drainage.

The Wax Ring

• The wax ring is exactly that: a ring of wax that sits underneath the toilet. When you install it, you can place it on the toilet horn, which is the discharge outlet underneath the toilet, or you can set it on top of the closet flange -- the disc that rests on top of the toilet drainpipe and connects to the bathroom floor. The toilet will not drain properly without this wax ring; instead, water will leak onto the floor, escaping out from underneath the toilet base every time you flush. The wax ring provides a watertight and airtight seal between the toilet bottom and the flange as water and waste drain out.

Pipe Size

• Always consult your local plumbing code to find out the minimum drainpipe size for all fixtures, including toilets, when you are installing new plumbing or replacing old or damaged pipes. Toilet drainpipes are either 3 or 4 inches in diameter. The closet flange will be either 3 or 4 inches, as well, and will be glued to the top of the closet bend directly underneath it or fitted over it and glued to the outside. The drainpipes on older toilets were often made of cast iron, which newer installations have replaced with PVC.

Slope

• The toilet drains by relying on gravity, not pressure. Because of this, the drainpipe that extends from the closet bend to the vent stack must slope downward slightly. This slope is generally 1/4-inch for every foot that the drainpipe runs. Without this slope, the toilet would constantly back up and not drain consistently as the water would just run around the waste, which would stop up the pipes. The vent stack is a vertical pipe that extends up through the roof into the open air. This is another vital component of the drainage system because it maintains atmospheric pressure within the drainpipes so the water and waste inside them flow properly.