Drip forms right under one tank bolt
One side of the tank-to-bowl area stays wet, and a drip forms directly below a single bolt.
Start here: Dry the tank and watch the matching bolt head inside the tank while the water level sits still.
Toilet leak troubleshooting
Toilet Tank Bolts Leaking
Direct answer: If toilet tank bolts are leaking, the usual cause is failed rubber tank bolt washers or loose tank hardware, but you need to confirm the water is actually starting at the bolts and not running there from the fill valve, supply connection, or a tank crack.
Most likely: Most often, the rubber washers inside the tank have hardened, split, or shifted, so water seeps down the bolt shank and drips underneath the tank.
Dry everything first and trace the first wet point, not the last drip. A lot of toilet leaks show up at the tank bolts even when the real source is a few inches higher. Reality check: a slow bolt leak can leave only a small puddle, but it can still stain flooring and rot the subfloor over time.
Don’t start with: Do not start by reefing down on the nuts. Overtightening is a fast way to crack the tank or distort the washers.
If the bolt heads inside the tank look wet first,suspect the toilet tank bolt washers or loose tank hardware.
If the bolts stay dry until after a flush or refill,look higher for a toilet fill valve leak, supply leak, or a hairline tank crack.
Last reviewed: 2026-04-05
What this toilet tank bolt leak usually looks like
Both tank bolts look wet
You see moisture or rust trails at both bolts, often with mineral crust around the hardware.
Start here: Check whether the rubber washers inside the tank are flattened, cracked, or off-center before tightening anything.
Leak shows up mostly after flushing
The area stays dry at rest, then drips during refill or right after a flush.
Start here: Look above the bolts for splash, a fill valve seep, or water tracking down from the flush valve area.
Water is near the back of the toilet but source is unclear
The floor behind the toilet gets damp, but you cannot tell if it is the bolts, supply line, or condensation.
Start here: Wipe the whole tank dry, place toilet paper around each suspect point, and identify the first spot that turns wet.
Most likely causes
1. Worn toilet tank bolt washers
These rubber washers sit inside the tank and seal around the bolts. When they harden or split, water follows the bolt through the tank hole.
Quick check: With the tank full and dry, look inside the tank at each bolt head. If water beads there first, the washer is leaking.
2. Loose or uneven toilet tank bolt hardware
If one side is tighter than the other, the tank can sit cocked and the washers will not seal evenly.
Quick check: Gently test for tank wobble by hand. If the tank shifts on the bowl, the hardware may be uneven or loose.
3. Water tracking down from the toilet fill valve or supply connection
A small seep above the bolts often runs along the tank wall and drips off the lowest hardware, making the bolts look guilty.
Quick check: Feel around the fill valve shank, supply nut, and nearby tank wall for moisture before the bolt area gets wet.
4. Hairline crack in the toilet tank near a bolt hole
Cracks often start around stressed bolt holes from age or overtightening and can mimic a bad washer.
Quick check: Use a flashlight and look for a fine line radiating from the bolt hole inside or outside the tank, especially if tightening changed nothing.
Step-by-step fix
Step 1: Shut off the water and find the first wet point
You need to separate a true bolt leak from water that is running down from somewhere else. That saves a lot of wasted parts.
- Close the toilet shutoff valve at the wall or floor.
- Flush the toilet and hold the handle briefly to empty as much tank water as possible.
- Wipe the tank, bolt areas, supply connection, and the top of the bowl completely dry with a rag or paper towels.
- Open the shutoff valve and let the tank refill while you watch closely with a flashlight.
- Use small strips of toilet paper around the fill valve base, supply connection, each bolt head inside the tank, and under each bolt outside the tank to see which spot wets first.
Next move: If you clearly see the first wet point, move to the matching repair path instead of guessing. If everything seems dry until after a flush, repeat the test during and right after flushing because splash or movement may be part of the problem.
What to conclude: A true tank bolt leak starts at the bolt head or washer area inside the tank, not just at the drip point underneath.
Stop if:
- The shutoff valve will not close fully.
- The floor is already soft, swollen, or badly stained.
- You find a visible crack in the tank.
Step 2: Confirm whether the leak is really at the toilet tank bolts
Bolt leaks and fill-side leaks look almost identical from the floor. Separate them early.
- With the tank full and sitting still, look inside the tank at each bolt head and rubber washer.
- Check for a bead of water forming around the bolt head, washer, or porcelain hole.
- Run your fingers carefully around the outside of the tank below the fill valve and around the supply connection nut.
- If the bolts stay dry at rest, flush once and watch for water splashing or running down from higher up.
- Look for rust streaks or mineral trails directly below one bolt, which usually point to a long-term washer seep on that side.
Next move: If one or both bolt heads inside the tank wet first, the tank bolt washers or hardware are the likely fix. If water starts above the bolts, stop chasing the bolt hardware and address the higher leak source first.
What to conclude: This tells you whether you are dealing with a tank bolt seal problem or a lookalike leak from the fill side or flush cycle.
Step 3: Try a careful, even snug-up only if the tank is intact
A slightly loose tank can sometimes be reseated with a small adjustment, but this is a light touch job, not a muscle job.
- Shut off the water and lower the tank water level again.
- Using the correct wrench or screwdriver setup for your hardware, tighten each side a little at a time so the tank stays level.
- Work in small increments, alternating sides instead of tightening one side all at once.
- Stop as soon as the tank feels stable and the washers compress slightly.
- Refill the tank and watch the bolts again for several minutes.
Next move: If the seep stops and the tank sits solid without rocking, monitor it over the next day and you may be done. If the leak continues, or the nuts are already snug, plan on replacing the toilet tank bolt set and washers.
Step 4: Replace the toilet tank bolt set if the washers are leaking
Once the rubber washers have aged out, tightening rarely lasts. Fresh tank bolt hardware is the durable fix.
- Shut off the water, flush, and sponge or towel out the remaining water from the tank.
- Disconnect the supply line if needed for access.
- Remove the old tank bolt nuts and lift out the old bolts, washers, and any corroded hardware.
- Clean the porcelain around the bolt holes with warm water and mild soap, then dry it fully.
- Install the new toilet tank bolts with new rubber washers inside the tank in the same sealing order provided with the kit.
- Set and tighten the hardware evenly side to side until the tank is stable and level on the bowl, then refill and check for leaks.
Next move: If the bolts stay dry inside and underneath during refill and after several flushes, the repair is complete. If new bolt washers still leak, inspect closely for a cracked tank or a leak from the flush valve area that is tracking toward the bolts.
Step 5: If the bolts are not the source, move to the right next fix
Water behind a toilet often gets blamed on the wrong part. Finish with the exact next action based on what you found.
- If water starts only during flushing and not at rest, inspect for water escaping from the tank-to-bowl connection or splashing over the rim path.
- If the leak begins at the fill valve shank or supply connection, repair that leak instead of replacing bolt hardware.
- If the toilet base rocks or the leak appears at the floor after use, the problem may be at the toilet base rather than the tank bolts.
- If you found a hairline tank crack, stop using the toilet until the tank is replaced or the toilet is professionally repaired.
- After any repair, dry the area completely and check again after several flushes and again a few hours later.
A good result: If the area stays dry through repeated flushes and refill cycles, you have the right fix.
If not: If the source still is not clear or the leak returns quickly, call a plumber before hidden floor damage gets worse.
What to conclude: The right repair depends on where the water starts. Common wrong move: replacing tank bolts when the real leak is a cracked tank or a flush-only leak from another seal.
Replacement Parts
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
FAQ
Can I just tighten leaking toilet tank bolts?
Sometimes, but only a little and only evenly side to side. If the rubber washers are old, tightening is usually temporary. Too much force can crack the tank.
Why do the toilet tank bolts look like the leak source when they are not?
Water from the fill valve, supply connection, or another tank seal often runs down the tank wall and drips off the lowest hardware. That makes the bolts look guilty even when they are dry at the start.
Do I need to replace both toilet tank bolts if only one is leaking?
Usually yes. If one washer has aged out, the other is not far behind, and replacing the full toilet tank bolt set keeps the tank level and the repair consistent.
Is a leaking toilet tank bolt an emergency?
Usually not in the first few minutes, but it should not be ignored. Even a slow drip can damage flooring, trim, and the ceiling below if the bathroom is upstairs.
What if new toilet tank bolt washers still leak?
Look closely for a cracked tank, a misassembled washer stack, uneven tightening, or water tracking down from the fill valve or center tank-to-bowl connection. New washers will not fix a cracked tank.
Should I caulk around the bolts or use sealant to stop the leak?
No. Sealant is a bandage here and usually hides the real problem. The fix is proper toilet tank bolt washers, correct hardware setup, or addressing the actual leak source above the bolts.