A.Terry Love, a plumbing contractor in Bellevue, Wash., responds: Most floors are a little uneven — with tile floors being the worst — so toilets often need to be shimmed when they're set. I like to set the toilet down first without wax to get a better idea of where the high and low spots are. Then, when I set the toilet, I use either a wax seal, which works well with older cast-iron and lead DWV systems, or the Fluidmaster Wax-Free Bowl Gasket (Fluidmaster, 949/728-2000, www.fluidmaster.com), which seems to work best with newer plastic waste lines.

To shim the toilet, I generally use cedar door shims because they have a more gradual taper than the plastic ones I've seen. I try to shim from back to front so that the front of the bowl is touching the floor, and from side to side so that the toilet is level. Shims usually end up at the back of the bowl, where they're held in place by the...

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