Prepare the Drain, Flange and Toilet Base
As necessary, clean out the drain plug to remove any debris or obstruction before installing the toilet (Image 1).
In our project, the drain was stuffed with paper before a wall tear-out began to prevent debris from falling in and the original toilet floor flange unit is in reasonably good shape.
Slide the retaining bolts (closet bolts) into place on the flange that will be used for the new toilet. The bolts should stick up from the floor, positioned for line up with the bolt holes in the toilet base.
The wax seal (Image 2) fits around the horn on the bottom of the toilet bowl and makes a very tight seal over the drain pipe.
Run a bead of clear silicon caulk around the toilet base as an added seal (Image 3).
If the flange is in bad shape, have a plumber replace it, especially if the flange is cracked or broken inside the inner circle where the wax ring forms a seal.
Caulk only the front of the bowl and leave the back uncaulked as an early warning sign for leaks.