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Question DetailsAsked on 5/29/2015

How much to replace seal between toilet tank and bowl?

Although there is no water on the floor or around the toilet, when I clean behind the toilet there is mold just below the tank in the back. I was told the seal between the bowl and tank needed to be replaced and it would cost $282. Is this reasonable? Should I replace the whole toilet instead?

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1 Answer


Assuming you mean the mold is on the toilet base itself, so you are sure that it is not a leaking pipe in the wall or leaking toilet wax seal leaking out from under the base onto or under the floor, then could be leaking tank seal but a lot more likely to be the mounting bolts or the gasket on the fill valve fitting into the tank. Slight tightening of them might stop it - do NOT reef on them, because you can crack the toilet - just snug should do it unless the bolts are corroding or the gaskets are shot and leaking.

Also, be sure the fill water in the tank (when filling) is warm and not dead cold outside ground temp water - cold water will make the tank "sweat", causing condensation to run down that might be causing your mold. If water is cold, you can clean tank/base more often to eliminate mold, or geat mixing valve put in (or fixed/replaced if you have one that is malfunctioning) for probably about $150 additional during plumber visit below - it "tempers" the water so it comes in warm to prevent sweating, which is caused by moist room air condensing moisture on the cold tank which has been chilled by the incoming cold water filling it.

Wipe well all around the bottom of tank and base of toilet with paper towels to thoroughly dry it, then after sitting on toilet and gently rocking a few times so it will move if it tends to in use, wipe under tank and around back of toilet base bit by bit with bare hand or toilet paper (which shows water better) to figure out WHERE the drip is coming from - if off bolts then almost certainly leaking bolt gaskets or corroded bolts, if off or around where flex tubing goes into bottom to fill valve try tightening that a bit, if coming off top of toilet base at gap between tank and toilet then could be bolts or the tank to toilet seal (which rarely leaks unless quite old).

Reason I said sit on it is that commonly the cause, unless just corroded away bolts, is the tank is touching the wall because of loose toilet base mounting bolts, tilted toilet installation, uneven floor, or floor joist sag, so when you sit on the toilet the toilet moves a bit and the tank tilts relative to the base because it is jammed against the wall, causing thetank mounting bolts to slack off and drip a little bit. Solution is resetting the tank to clear the wall, or in extreme cases resetting the toilet to avoid touching the wall, which if it is doing it hard enough can eventually cause the bolts to break out the bottom of the tank or the slots in the toilet base, causing a flood and mandating toilet replacement.

Unless you are in a very high-priced major city like Boston, NYC, SFO, West LA, etc - I would say that price is about double normal for that scope, so get another estimate. Replacing tank-to-toilet seal, bolts and bolt gaskets only would usually be about $10-25 parts and minimum service charge time - about $90-150 typically except in very high priced cities. IF resetting/relevelling the toilet is required, at same time, (which requires new wax seal and should include new mouting bolts too) add about $10-15 materials and maybe 15-30 minutes more work, so maybe another $50-100 range added onto your cost.

Unless you find a crack in the tank or the slots/holes for the bolts are broken away, no reason to replace toilet.

Answered 5 years ago by LCD

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