You've finished laying the new bathroom floor, but now you find a problem: The floor is uneven where the toilet will be installed. Not as uncommon as you might think, installing a toilet on an uneven floor will take a few hardware items and some common household tools. Roll up your sleeves and put your knee pads back on; before you know it you'll be flushing your cares away, uneven floor or not.
Tip the toilet on its side and install a new wax ring seal in the drain hole, then carefully set the toilet onto the drain hole, making sure the flange bolts come through the holes on the sides of the toilet.
Lay a level lengthwise on the back of the toilet tank, then sit backward on the toilet, straddling the bowl and shifting your weight to make the toilet level. The object is to seat the wax ring while levelling the commode; the seal must not be broken once it has been seated, so do not rock from side to side.
Insert the hard rubber shims beneath the toilet on the side or sides that are uneven, working your way around the bowl according to the reading on the level until the toilet is level. The shims should be inset 1/4 inch from the outside edge of the toilet.
Bolt the toilet down, using the two bolts on the sides of the toilet to secure it firmly. Do not over-tighten, as this may crack the porcelain.
Connect the water line to the toilet intake and turn on the shut-off valve that is located near the floor. Check for leaks at the plumbing connections and tighten if necessary.
Run an even line of caulk around the base of the toilet, sealing the unit to the floor and hiding the shims.
Some plumbers recommend leaving a small area in the back of the toilet without caulk in order to detect leaks as soon as they occur. Some plumbers prefer hard plastic shims over hard rubber shims.