Replace a leaking toilet tank gasket
Renew the tank-to-bowl seal and bolt washers on a standard two-piece toilet.
Home · 1–2 hr · Medium
Before you start
Shut the supply off and drain before unbolting. Have a helper support the heavy tank; never rest it on projecting fittings. Stop for cracked porcelain or seized bolts. Do not use power tools or pull the tank hard against the bowl to cure a leak.
Tools and materials
- Exact-fit tank-to-bowl gasket and compatible tank bolt/washer kit
- Adjustable wrench, matching screwdriver and padded support
- Bucket, sponge, towels, gloves and eye protection
Check the problem
Find where the water starts
Dry the tank, supply and bowl ledge. Watch at rest and during one flush. Moisture from the supply or tank exterior can run toward the seam; a leaking bolt seal is different from the large outlet gasket.
Identify the gasket and hardware
Use the toilet model information and parts drawing to select the gasket profile and bolt kit. Diameter alone is not enough. Check that the bolt heads and nuts are accessible before starting.
Steps
Isolate, empty and disconnect
Close the valve, flush and verify the tank does not refill. Sponge it dry, set the lid on padding and disconnect the supply into a bucket.
Support and lift off the tank
Hold the bolt heads while undoing the nuts. A helper must steady the tank. Lift it clear and place it on a padded, stable surface with fittings protected; leave the bowl fixed to the floor.
Clean and inspect the sealing area
Remove the old gasket and bolt seals. Wipe the outlet and sealing surfaces clean. Stop for cracks or a leaking/loose flush-valve mounting joint; that needs a different repair.
Install the matching seals and bolts
Seat the new large gasket over the flush-valve mounting nut as specified. Assemble new bolts and washers exactly as the kit shows, with rubber sealing against the tank at the water-sealing holes.
Reseat and tighten evenly
Lower the tank into position without rolling the gasket. Fit the lower hardware and tighten alternately in small increments while a helper holds it level. Follow the specified tank-to-bowl spacing; do not force porcelain contact.
Reconnect and test at rest and flushing
Reconnect the supply as specified and open the valve slowly. Check the supply, bolt ends and seam as the tank fills, at rest and through several flushes. Shut off again if any joint becomes wet.
No moisture at the supply, tank bolt ends or tank-to-bowl seam at rest or through repeated flushes; tank remains stable.
Tips
Do not reuse flattened seals
Replace worn bolt seals along with the main gasket using compatible parts.
Keep weight off the fittings
Set the tank on padding that supports porcelain rather than the fill-valve shank or outlet.
Do not solve every drip by tightening
Recheck alignment and seal selection if leaking persists. More force can crack the tank.