How to Fix a Leaking Toilet Tank

As a rule of thumb, you should always turn off the water before working on any plumbing project. Locate the water supply valve next to your toilet and turn it off. You may need gloves for a stronger grip to turn the valve completely. Now, remove the tank lid and flush the toilet. You won’t see water refilling the tank if the water is off.

You can skip this step if you’d rather replace all old parts with new ones you’ve purchased.

Mark the water level with a pencil or marker. Grab some water-dye tablets from your local hardware store, or use food coloring. Wait at least 10 minutes for the water in the tank to change color completely. Now, check the water in your toilet bowl. If it also shows a color change, the water in your tank leaks into the bowl through the flush valve.

Next, check the water level. If it has risen beyond the mark you made, you might have a faulty fill valve. Another indicator is if you see water leaking from the flush handle. That happens when the water level rises beyond the handle connector because the fill valve isn’t working properly.

Finally, see if the dyed water has leaked onto the floor. If the leak comes from the bottom of the tank, you might have a leaky gasket. However, if water is coming out of the tank body, you have a cracked tank, and it’s best to replace it completely.

Flush the toilet to empty the water and use a big sponge to soak up whatever is left in the tank. You want a dry working environment since you are taking the tank apart. Unscrew the bolt to disconnect the water supply line from your tank. The supply connection is usually on the far left.

If the only problem is a faulty fill valve, you can complete the replacement without removing the tank. Remove the existing fill valve with two adjustable wrenches. Then, insert the new fill valve following the manufacturer’s instructions. You may want to tighten the bolts a quarter turn for secure fastening. Turn on the supply line and check for leaks.

If the leak is happening at the bottom of the tank or into the toilet bowl, you will need to remove the tank. Having a helper for this step will make it go much faster.

Hold down the nut underneath the tank with an adjustable wrench with the water supply disconnected. Unscrew the bolt on the inside with a regular screwdriver. Remove the second bolt with the same process.

Carefully remove the tank and lay it down with the bottom facing you.

Follow the manufacturer’s instructions to replace the toilet flapper. Most toilets can use a universal flapper kit available at any hardware store. Now, look at the bolts you removed. You should find a rubber gasket on each one. These gaskets deteriorate over time. Therefore, you should replace them with new ones when you remove the tank.

Meanwhile, soak the metal washers, nuts, and bolts in vinegar to clean any build-up. If you haven’t opened the toilet tank during the past six months, you may want to replace all bolt parts.

Remove the big rubber washer in the middle of the tank by turning it with your hands. That’s your spud washer. If the washer seems stuck, try using an adjustable wrench to remove it.

Now, install the new spud washer. You definitely want to use a wrench for the new washer for sufficient tightening. You can also apply some caulk around the edge for a stronger seal.

Now, reinstall your toilet tank and reconnect the water supply hose. Repeat step 2 with food coloring or water dye to ensure you have successfully repaired the leak. If you still see colored water coming out of the tank or into the toilet bowl, you may consider hiring a professional for the repair job.