A wax ring on a toilet creates a seal between the toilet outlet and the waste flange. Without the ring, toilet water and waste may leak from beneath the toilet. When a toilet is replaced, some of the wax remains stuck to the toilet, and what's left on the flange may be smudged. Because the ring is such an important leak guard, the wax ring must be replaced whenever a new toilet is installed or the toilet is removed for any reason.
Styles and Sizes
Wax rings are available with no backing, or a plastic sleeve to direct waste into the drain. Toilets are installed with 3-inch drain pipes, so wax rings are one size fits all with regards to diameter. Thickness varies, due to the fact that the drain may be installed lower than the floor, and the ring must meet both the drain and the toilet flange.
Measuring for the Ring
You should check the distance between the drain flange and the level floor. Note whether there's a large gap that may result in the need to buy a thicker ring or multiple rings without backing. Once you get to the hardware store, compare the thickness of the ring with the distance you measured and purchase accordingly.
Once you have scraped the old ring from the drain flange and attached the brass closet bolts, you can carefully press the wax ring over the flange. The flat side faces the floor, and the rounded edge points toward the toilet. Put the toilet on top of the ring. Keep the bowl as straight as possible to avoid smudging the wax and compromising the seal. Continue with toilet installation.