Sealant is usually the wrong response to an active toilet leak. Water can escape from the supply connection, fill-valve shank, tank bolts, tank-to-bowl gasket, floor seal or cracked porcelain. Smearing material around the visible wet edge can hide the first leak point while water continues to damage the floor.
This page is a diagnosis guide based on Fluidmaster’s leak-location guidance. It intentionally has no affiliate product module because the failed component must be identified before a safe purchase can be made.
Stop use and contain the water
Close the toilet’s local shutoff valve. If it does not stop flow, close the home’s main shutoff. Mop up water and protect the room below. Do not refill or flush the toilet while the source is unknown.
A cracked porcelain fixture should be taken out of service and replaced. A rocking bowl also needs prompt attention because movement can disturb the floor seal and damage the flange or subfloor. Exterior caulk cannot stabilize it.
Inspect without operating the toilet
Dry the tank, bowl exterior, supply connector, valve and floor. Look for mineral tracks, corrosion, loose hardware and dampness from top to bottom. Check the supply valve and connector, the fill-valve shank, tank bolts, and the joint between the tank and bowl. Water travels along porcelain, so the puddle location alone does not identify the failed part.
If the fixture must be operated to reproduce the leak, leave that controlled test to a plumber or another qualified person who can isolate the water immediately. Continued trial flushing is not a diagnostic plan.
Match the repair to the failed component
A leaking connector, fill-valve seal, tank bolt or tank-to-bowl gasket needs the correct replacement part and a model or dimension check. Water found at the base can involve the floor seal, flange, unstable mounting or damaged flooring; resolving it commonly requires removing the toilet and inspecting the concealed parts.
For a leak at the tank-to-bowl joint, replace the gasket and bolts as a set. Korky’s 464 kit (also sold as 464BP) is one example: a sponge gasket for a 2-inch flush-valve opening plus three stainless bolts with rubber washers, metal washers and nuts. Korky says it fits most 2-inch two-piece tanks. The gasket has a 2-1/8-inch inside diameter, so a larger flush valve needs a different one, and a one-piece toilet has no tank-to-bowl joint at all. This kit won’t stop a supply, fill-valve or floor-seal leak.
Do not overtighten fasteners against porcelain. Tighten evenly and only as the fixture or repair-part maker directs. Replace damaged or questionable supply components rather than coating them with sealant.
When caulk belongs at the base
Local installation rules may call for a sanitary bead around part of a correctly installed toilet base. That finish bead is not the concealed floor seal and must not be used to cover an active leak or hold a moving bowl in place.
Use a plumber when the shutoff will not close, the flange or floor is damaged, the leak reaches another level, porcelain is cracked, or the source remains uncertain.
Primary source: Fluidmaster toilet-leak troubleshooting .
Gasket kit source: Korky 464 2-inch tank-to-bowl gasket and hardware kit .