Toilet Tank Leaks at Bolts: Common Fixes
Short answer: If water collects around the tank bolts or runs down the side of a two-piece toilet, the leak comes from the tank-to-bowl seal, not from the plumbing inside the tank. Remove the tank, replace the old bolts, rubber washers, and the tank-to-bowl gasket, then tighten the nuts evenly. If the porcelain is cracked around a bolt hole, replace the toilet rather than trying to patch it.
What a tank bolt leak looks like
A two-piece toilet has a separate tank and bowl joined by tank bolts. The bolts pass through holes at the bottom of the tank, and each one is sealed with rubber washers and a gasket before it reaches the bowl. When those seals age, water finds its way out of the tank. You may see dampness around the bolt heads, drips on the outside of the tank, or a small puddle on the floor.
Because the tank is full of water after every flush, a slow bolt leak can appear only after the toilet is used. Rust-colored streaks running down the tank or bowl usually mean the bolts or washers have corroded. If you are not sure where the water is coming from, also check the floor around the base of the toilet: a leak in that spot is a separate problem. See how to fix a toilet base leak to compare the two locations.
Most toilet-related water waste is not from leaking tank bolts. According to the EPA, household leaks can waste 180 gallons per week, and toilets are often the culprit, with worn flappers the most common cause. If water is running into the bowl rather than dripping down the tank, start with the running toilet guide instead.
Why tank bolts leak
The usual cause is a rubber washer that has lost its flexibility. After years in water, a washer can harden, flatten, or split, and it will no longer seal the bolt hole. Bolts made from plain steel can corrode at the same time, and rust can damage the washer from underneath. Corrosion is covered in more detail in the tank bolt corrosion guide.
Uneven tightening also causes leaks. If one nut is tighter than the other, the tank tilts slightly and the tank-to-bowl gasket does not sit evenly. Over-tightening is just as bad because it can crush the washers or crack the porcelain around the bolt hole. A hairline crack may not leak at first, but it can grow with normal use.
- Worn or brittle rubber washers under the bolt heads
- Corroded bolts or nuts
- A damaged tank-to-bowl gasket
- Uneven or excessive tightening
- A cracked tank or bowl around a bolt hole
How to reseal tank bolts
The permanent fix is to take the tank off and replace the seals, not simply to tighten the nuts. Close the water supply and flush the toilet to empty the tank. Disconnect the supply line, then remove the nuts under the bowl that hold the tank down. Lift the tank straight up and set it on a padded surface so the bolts and the tank rim are not damaged.
Turn the tank over to expose the bolt heads. Remove the old bolts, rubber washers, and any putty or sealant left around the holes. Clean the holes and the tank floor so the new washers sit flat. Install new bolts with fresh rubber washers, placing the sealing washer under each bolt head, then set the tank back on the bowl over a new tank-to-bowl gasket. See how to install toilet tank bolts for the tank-side details.
Thread the nuts onto the bolts from below and tighten them in an alternating pattern. Go snug, then stop after a firm turn. Watch the tank as you work to keep it level. Reconnect the supply line, open the water valve, and let the tank refill. Flush a few times and check the bolt heads and the seam under the tank for dampness. If the seam still weeps, the tank-to-bowl gasket is the part to replace.
When to replace bolts, washers, and the gasket
Plan to replace the tank bolts and washers any time you take the tank off. They are inexpensive parts, and reusing old washers is the quickest way to end up with a second leak. Replace both bolts rather than one. If the originals showed rust, choose stainless steel hardware; stainless steel resists corrosion far better than plain steel in the damp space inside the tank. The brass vs. stainless steel bolts guide explains the material choices.
The tank-to-bowl gasket is the large rubber ring that seals the opening between the tank and bowl. It can flatten or harden even when the bolts look fine, so if the first reseal does not stop a leak at the seam, replace the gasket at the same time. A failing gasket is a common reason water appears around the underside of the tank.
Tightening existing bolts may slow a drip for a while, but it is not a substitute for a proper reseal. If you see cracks in the porcelain around a bolt hole, stop tightening. Porcelain cannot be patched reliably, and further tightening can turn a small crack into a break that empties the tank onto the floor. See tank crack replacement before deciding on a repair.
How to tell a bolt leak from other toilet leaks
Confirm that the leak is actually at the bolts before removing the tank. Water at the seam where the tank meets the bowl can come from the tank-to-bowl gasket. Water around the base of the toilet on the floor usually points to the bowl gasket or wax ring. Water that keeps running into the bowl is a flapper or fill valve problem and may not wet the floor at all.
| Where water appears | Likely part | First check |
|---|---|---|
| Damp around the bolt heads or down the outside of the tank | Tank bolt washers | Inspect washers and reseal the bolts if they look old |
| Water at the seam between tank and bowl | Tank-to-bowl gasket | Replace the gasket when resealing the tank |
| Puddle around the base of the toilet | Bowl gasket or wax ring | Check the base and floor flange |
| Water constantly flows into the bowl | Flapper or fill valve | Start with the flapper guide |
| Drops on the outside of the tank on humid days | Condensation | Dry the tank surface and manage room humidity |
Preventing tank bolt leaks
A resealed tank can stay dry for years if the bolts are installed correctly. Keep the tank level, do not overtighten the nuts, and use new washers whenever you open the tank. A small amount of plumber's grease on the rubber washers can help them seat, but do not rely on caulk or silicone to stop a leak; the rubber seals do that work.
Check the tank occasionally for dampness around the bolts and for rust streaks. Cleaning the tank interior removes mineral buildup that can speed up corrosion. If you are replacing other parts such as the flapper, inspect the tank bolts at the same time.
If you are shopping for a new toilet and want to remove the tank-to-bowl seam from your list of worries, a one-piece toilet has the tank and bowl cast as a single unit, so there are no tank bolts to leak. That is one reason buyers compare best one-piece toilets when replacing a two-piece fixture.
When to replace the toilet instead
Resealing handles most tank bolt leaks, but it cannot fix cracked porcelain. If the tank or bowl is cracked at a bolt hole, replace the toilet. The same is true if the leak returns after a careful reseal and you cannot find a practical cause; the fixture may be damaged internally.
Replacement is also worth considering when an older toilet is leaking and inefficient. The EPA notes that older inefficient toilets can use as much as 6 gallons per flush, while WaterSense labeled toilets use 1.28 gallons per flush or less. Toilets are the largest source of indoor water use in a typical home, so a leaking fixture can waste a meaningful share of the more than 300 gallons the average American family uses at home each day, with roughly 70 percent of that use indoors.
If you decide to replace, compare WaterSense labeled models and consider the best 1.28 GPF toilets as a starting point.
What to pick for your use
| If you | Pick | Buying guide |
|---|---|---|
| You are replacing the toilet because the tank is cracked around a bolt hole | A two-piece toilet for the easiest swap | Best Two-Piece Toilets in 2026: 15 Picks Compared on Specs |
| You want to remove the tank-to-bowl seam entirely | A one-piece toilet | Best One-Piece Toilets in 2026: 15 Picks Compared on Specs |
| Your leaking toilet is old and inefficient | A WaterSense labeled 1.28 GPF model | Best 1.28 GPF Toilets in 2026: 15 Picks Compared on Specs |
| You are replacing and want easier stand-up use | A chair height toilet | Best Chair Height Toilets in 2026: 12 Picks by Specs |
| You are replacing and want a model that fits the most common floor opening | A toilet with a standard rough-in | Best 12-Inch Toilets in 2026: 15 Picks Compared on Specs |
Questions
Can I fix a tank bolt leak without removing the tank?
Usually not. The sealing washers sit under the bolt heads inside the tank and under the nuts below the bowl, so the tank has to be lifted to reach them. Tightening the nuts may slow a drip temporarily, but old washers will keep leaking.
Why does my toilet still leak around the bolts after I tighten them?
Tightening does not restore a hard or split rubber washer. The washer has to be replaced. If the leak is at the seam rather than at the bolt heads, the tank-to-bowl gasket is probably the cause.
Should I use plumber's putty or silicone on the tank bolts?
The rubber washers and tank-to-bowl gasket are the sealing parts. Putty or silicone is usually unnecessary and can prevent the tank from seating evenly. If the manufacturer includes a sealant with the replacement kit, follow its instructions.
Do one-piece toilets have tank bolts that can leak?
No. A one-piece toilet has the tank and bowl molded as a single unit, so there is no tank-to-bowl seam and no tank bolts. The bolt leak problem is specific to two-piece toilets.
How can I tell a bolt leak from a base leak?
A bolt leak normally appears around the tank bolts or on the outside of the tank and bowl above the floor. A base leak appears as a puddle around the bottom of the bowl and usually involves the bowl gasket or wax ring at the floor flange.
Is a cracked tank around a bolt hole repairable?
No. Porcelain cracks around a bolt hole are structural, and no patch can safely seal them. Replace the toilet so the tank does not fail under pressure.
Revision notes
- : First published.