What you need to do before you start

Toilet tank bolts corrode, crack, or strip over time, and replacing them stops leaks where the tank meets the bowl. The job takes about 30 minutes and requires only basic tools — you do not need a plumber. The bolts sit underneath the tank, so you will need to drain the water first, then unbolt the tank from above and below.

Before you begin, turn off the water supply valve behind the toilet (turn the knob clockwise). Flush to empty the tank, then use a sponge or towel to soak up any remaining water inside the tank. This keeps you dry and prevents water from spilling onto your floor.

Key Takeaways

  • Toilet tank bolts are located underneath the tank where it connects to the bowl, and you access them from below the toilet.
  • You will need a wrench or socket set, a screwdriver, and replacement bolts (usually sold as a kit with rubber washers and metal washers).
  • Drain the tank completely before you start, and work from underneath the toilet to loosen the old bolts while holding the nut from above.
  • New bolts should be hand-tightened first, then tightened with a wrench only until snug — over-tightening cracks the porcelain bowl.

Getting underneath the toilet to see the bolts

The bolts run vertically through the base of the tank and into the bowl. To reach them, you need to get under the toilet. If your toilet sits on a pedestal base, you can kneel or lie on your back on the floor and look up. If it sits on a cabinet or vanity, you may need to remove the cabinet panel or work from the side.

Use a flashlight to see the bolts clearly. There are usually two or three bolts, each with a nut on the underside. The bolts may be corroded or stuck, so spray them with penetrating oil (like WD-40) and let it sit for 5 to 10 minutes before you try to loosen them.

Removing the old bolts

From underneath the toilet, use a wrench or socket to hold the nut steady while you unscrew the bolt from above. This two-person approach — one person turning the bolt, one holding the nut — is easiest, but you can do it alone by holding the nut with one wrench and turning the bolt with another.

If a bolt is stuck, explore more penetrating oil and wait longer. Do not force it; a broken bolt left in the hole is harder to remove than a stuck one. Once the nut comes loose, unscrew the bolt by hand and remove the rubber and metal washers underneath. Keep these washers as a reference for the new ones.

Repeat for each bolt until the tank is free. Lift the tank straight up and set it on a towel on the floor or on the closed lid of the toilet seat. Do not tip it sideways — the porcelain is fragile.

Choosing and installing new bolts

Toilet tank bolt kits are sold at hardware stores and online retailers. A standard kit includes two or three bolts (usually 5/8 inch or 3/4 inch diameter), rubber washers, and metal washers. Check the diameter of your old bolts with a ruler or caliper before you buy, or bring an old bolt to the store to match it.

Slide the new bolt through the hole in the bowl from underneath, then place the rubber washer on the bolt (rubber side down, against the porcelain), then the metal washer. Lift the tank back into place and align the bolt holes. Slide the bolt through the tank hole and thread the nut onto the bolt by hand.

Tighten the nut with a wrench, but stop as soon as it feels snug. Porcelain cracks easily if you over-tighten. A good rule: tighten until you feel resistance, then turn the wrench one more quarter turn. Repeat for each bolt, alternating between them so the tank sits evenly.

Checking for leaks and reconnecting water

Once all bolts are tight, turn the water supply valve back on (turn counterclockwise). Let the tank fill, then flush once to check that water flows normally. Look underneath the toilet where the tank meets the bowl. If you see water dripping from the bolt holes, the bolts may be too loose — tighten them slightly and check again.

If water still leaks after tightening, the rubber washers may be damaged or the bolts may be the wrong size. Turn off the water, drain the tank, and remove the bolts again. Replace the rubber washers with new ones from a hardware store, or buy a new bolt kit and try again.

Tools and materials you will need

A wrench or adjustable wrench works for most bolts, though a socket set gives you better grip and control. You will also need a screwdriver (usually flathead) to help pry off old washers, a flashlight, penetrating oil, and a sponge or towel. Wear old clothes or an apron — you will get wet.

The replacement bolt kit is the main material cost, usually between $8 and $15 at a hardware store. Some kits include extra washers and gaskets for the fill valve or flapper, which is useful if you are already working on the toilet. If you cannot find a kit, you can buy bolts, washers, and nuts separately at the same store.

What to do if a bolt breaks or won't come out

If a bolt snaps while you are removing it, the broken piece stays in the hole. Use a pair of locking pliers or a bolt extractor tool to grip the broken end and turn it counterclockwise. If that does not work, drill out the bolt with a drill bit slightly smaller than the bolt diameter, then use a screw extractor bit to remove what is left.

If you do not have these tools, a plumber can remove a broken bolt in 15 minutes for a service call fee. For a first-time repair, it may be worth calling rather than buying tools you will use once. However, if you plan to maintain the toilet yourself over time, a basic bolt extractor set costs $10 to $20 and will last for years.

Frequently Asked Questions

How tight should the bolts be?

Tighten until snug, then stop. The bolts only need to hold the tank in place and compress the rubber washers — they do not need to be as tight as a car wheel. Over-tightening is the most common mistake and causes cracks in the porcelain bowl that lead to leaks you cannot repair.

Can I replace just one bolt or do I need to replace all of them?

You can replace one bolt at a time if only one is leaking. However, if the others are corroded or cracked, they will fail soon after. Most people replace all bolts at once to avoid the job twice in a short time.

What if the bolt holes in the bowl are cracked?

A cracked hole cannot hold a bolt, and the tank will leak no matter how tight you make it. The bowl itself must be replaced. This is a larger job that usually requires a plumber, as it involves disconnecting the water supply, removing the tank, and installing a new bowl.

Do I need to turn off the water before I start?

Yes. If you do not turn off the water, the tank will refill as you drain it, and you will have water running down your back while you work underneath. The water supply valve is behind the toilet, usually on the left side, and turns clockwise to shut off.

How long does this repair take?

For someone doing it for the first time, plan on 30 to 45 minutes. Most of that time is waiting for penetrating oil to loosen corroded bolts. If the bolts come out easily, the job takes 15 minutes.