A Toilet Leaking at the Base

If the floor is dry until a flush and wet shortly after, water is escaping between the bottom of the toilet and the drain. That is the wax or rubber seal the fixture sits on, and it means lifting the toilet to replace it.

This is the one not to leave. Water escaping there goes under the fixture and into the floor, where it is doing damage nobody can see until the floor moves.

A wet patch behind the toilet that is there whether or not anyone has flushed is the supply line, its connection to the fill valve, or the shut-off valve itself. All three are above the floor and visible. Drying everything and watching which fitting beads first identifies it in minutes.

On a two-piece toilet the tank bolts to the bowl through a large rubber gasket. When that perishes, water runs down the back of the bowl and reaches the floor at the base — which looks exactly like a seal failure and is not. Feeling the back of the bowl while someone flushes tells the two apart.

In a humid bathroom, cold water in the tank makes the outside of the porcelain condense, and it drips onto the floor. It is worst in summer, worst in rooms without ventilation, and it produces a wet floor with nothing broken.

The test is timing: condensation appears gradually and is worst when the room is warm and humid; a seal leak appears after a flush. Getting this wrong is how people pay to have a working toilet lifted.

If the fixture moves when you sit on it, treat the leak as the second problem. Movement breaks the seal, and replacing the seal without fixing what is letting it move puts you back here in a year.