Toilet Leaks Only When Flushed: How to Fix Base and Tank Leaks

A leaky toilet is a headache for homeowners, although it’s something easy to repair once you know where to start.

If a toilet leaks when flushed, it’s usually due to a worn wax ring, closet flange, or tank gasket.

Those are the main reasons you’ll find why a toilet leaks when flushed, but not the only ones. Shutoff valves can be problematic, along with other hidden issues below or inside the tank. 

If you’re ready to attempt a repair and avoid the plumber, our guide will have your floors dry and the toilet fixed in no time.

Why Does a Toilet Leak When Flushed?

We outlined a few of the more common ways a toilet can leak when flushed, but the source of the leak can tell you a lot about what’s going on.

Does the toilet leak from the bottom with every flush?

If so, it could be an issue with loose bolts. This can happen if you’ve recently installed a commode or had one repaired. It’s also not uncommon for toilet bolts to become loose when people stand on seats.

Wax rings can dry out, causing toilets to leak from the base, but are you sure the leak is from the  base and not higher up?

Water runs downwards from a leak, so the bowl or a leaking toilet tank could be the culprit. Whatever the problem may be, here’s how to find the leak and fix it.

How To Fix a Toilet That Leaks Only When Flushed

The first step is to try and find the leak. Wipe the toilet down to ensure it’s free of condensation, and get a towel ready to keep water off the floor. Give the toilet a flush, and watch the outside of the toilet tank and bowl.

You may see a noticeable trickle coming from an area, including a crack in the bowl or toilet tank.

You can patch minor cracks above the waterline with a special epoxy in some cases. If it’s enough damage to cause a leak, the best option is to replace the toilet bowl or tank if it’s a two-piece model.

If you see water dripping from the water supply line, you can try to tighten up the locknut on the bottom of the tank by hand if it’s loose.

If that doesn’t do the trick, you’ll want to round up the following tools and supplies.

The parts you’ll need depend on the issue, but everything is affordable and easy to acquire locally or online.

Tools & Supplies

• Adjustable wrench
• Locking pliers
• Flathead screwdriver
• Putty knife
• Rubber gloves
• Bucket
• Sponge and Rags
• Bathroom cleaner

Parts

• Wax Ring
• Tank to bowl gasket
• Closet flange
• Toilet bolts

How To Fix a Toilet Leaking at the Base When Flushed

When you have a toilet that wiggles when you sit and leaks from the bottom, you may just need to tighten up the tank bolts.

Remove the toilet bolt caps from each side of the commode using a putty knife if needed.

If they seem loose, simply tighten each one “evenly” and do not over-tighten the bolts. Give the toilet a test flush; if you don’t see a leak, job well done.

If the issue isn’t the bolts, grab an assistant as it’s time to drain the toilet and remove it from the floor.

Step 1: Shut off the Water Supply Valve

Locate the water supply shutoff valve for your toilet and turn it off. It should be behind the commode on the wall and easy to turn. If it’s stubborn, don’t force it but try a little WD-40 instead.

Step 2: Empty the Toilet and Tank

Remove the lid from your toilet tank and give it a flush. As you can see, the tank doesn’t fill back up, and you can hold the lever down to try and get all the water out you can.

Put your gloves on, and use the sponge to remove any excess water from the toilet tank and squeeze it into your bucket or container. Use the same process to eliminate any water remaining in the toilet bowl.

Step 3: Remove the Water Supply Line

Remember that valve you shut off? Now you need to disconnect the end of the hose running from the valve from the toilet tank.

You should be able to loosen the nut that connects the supply line to the fill valve with your hands. Use the adjustable wrench with a rag to protect the plastic nut if it’s too tight.

Step 4: Remove the Toilet Tank

If you have a one-piece toilet, you can skip ahead to the next section. Otherwise, loosen the tank from the mounting bolts using a wrench.

A ratchet with the right-size socket will speed the job up, but make sure all the nuts are removed.

Using assistance, carefully lift the tank from the bowl and set it out of the way. We recommend placing it on an old towel to keep your bathroom floor and the tank safe.

Step 5: Loosen Toilet Bolts

Take a putty knife and remove the bolt cap covers from the toilet. They can be tricky, but this guide will show you how to safely pull them off and put on new ones if yours are worn.

The nuts holding the tank in place should unscrew with a wrench. If they are stubborn, you can loosen them up with a blast of WD-40.

Step 6: Remove the Toilet Bowl

Removing the bowl is another step that may require help, especially if you intend to move the toilet out of the bathroom temporarily.

Straddle the toilet and gently rock it from side to side to break the seal around the bottom. If there’s caulking, use the putty knife to remove it. Once loose, take a rag and put it into the drainpipe to keep sewer odors from getting into your home.

Place the toilet on its side and remove any residue from the old wax ring on the commode. Use the same process to remove any excess wax from the flange around the drain pipe.

Step 7: Inspect the Flange

If the flange is in good shape with no visible cracks or damage, you’re good to go and can skip ahead to the next section in our guide. If the floor bolts or flange is worn or looks like they could need to be replaced, now is the time to do it.

Toilet bolts are easy to replace, but a closet flange can be challenging to work with. That’s because they could be glued or even welded onto the pipe, making them nearly impossible to remove in cramped quarters.

This can be an issue in homes with older plumbing and is where you’ll need to call a plumber unless you have a flange that’s easy to remove with only a handful of screws.

If that’s the case, you can follow these steps to remove and install a new toilet flange.

Step 8: Replace the Wax Ring

With the flange and wax ring free of debris, it’s time to install the new ring and remove anything you used to block the drain. It’s critical that all the old wax ring is removed beforehand to get a tight seal.

These rings come in 3 and 4-inches depending on the size of your drain pipe and two thicknesses. If the toilet flange is recessed, you may need a thicker ring than a standard one.

You can install the ring by placing it directly onto the flange or around the bottom of the bowl, as shown in the video below.

Step 9: Reseat the Toilet & Attach the Tank

With the wax ring in place, it’s time to reseat the toilet. Pick the toilet up and place it over the flange with the bolt holes lined up with the bowl.

Press down firmly on the bowl to set the ring and create a water tight seal, but do not tilt or move the toilet from side to side.

With the toilet in place, take the nuts you removed from your toilet and place them back onto the bolts. Screw them down until they are snug. Use the wrench to tighten down each side, alternating every few turns until it’s nice and tight.

You’ll need to replace the tank the same way you removed it for two-piece toilets. Make sure the tank to bowl gasket is firmly attached, then put the bolts and washers into place. Align the tank over the holes in the bowl and gently set it down.

Tighten the tank bolts as you did with the toilet bolts. Take turns to get a nice, even fit until the tank is in place.

Step 10: Test for Leaks

When you’re satisfied the toilet has been properly seated, and the tank is set, it’s time to hook up the supply line. Simply screw the supply hose back into the fill valve on the bottom of the tank and firmly screw the nut down until it’s tight.

Turn the water on at the supply valve behind the toilet slowly and let the toilet tank fill up. Flush the toilet and look at the base to check for any leaks. Give it a few minutes and a few flushes, but keep an eye on the supply line connection and the area where the tank meets the bowl on two-piece commodes.

If you don’t see any water on the floor around the bowl, clean up the area with a bathroom cleaner and enjoy your leak-free commode.

How To Fix a Toilet Leaking Between Toilet Tank and Bowl When Flushed

When a toilet leaks between the toilet tank and bowl, you’ll need a new gasket unless the bolts are loose. This process is easier than replacing rings and flanges, although you’ll still need to drain the tank and remove it from the bowl.

Step 1: Turn off the Water and Drain the Tank

Turn off the water at the toilet valve behind the tank, remove the toilet tank lid and give the toilet a flush. When the tank is drained, take a sponge and soak up any remaining water.

With the tank completely empty, detach the nut holding the water supply line to the toilet.

Step 2: Remove the Tank and Gasket

Take a wrench and loosen the bolts on the bottom of the toilet tank. Once the toilet tank is loose, remove it and set it on its side so you can access the tank to bowl gasket.

Unless you know what kind of gasket you need and have one on hand, you’ll want to take the old gasket to a hardware store and pick up a new one that fits your commode. There are also toilet tank kits that can cover a few sizes but not the entire range.

Step 3: Replace the Gasket and Tank

Using a putty knife, make sure no residue is on the bottom of the tank, then place the tank to bowl gasket back into place on the bottom of the toilet tank.

Put the tank into place, and then put the bolts and any washers you removed back before grabbing the locknuts. Use the wrench to tighten up the tank, taking care to alternate between bolts until the toilet tank is firmly back in place.

Step 4: Check for Leaks

Take the end of the water supply line and reattach it to the tank. Screw the nut on tightly before slowly turning on the water supply.

When the toilet tank fills, flush it and look for any leaks between the bowl and the tank. If you followed our steps and chose the correct gasket, your job should be complete.

The Bottom Line

Toilets that leak when flushed are a problem that can get overlooked if it’s only a trickle or a seldom-used commode in a secondary bathroom.

Doing so will lead to bigger issues down the road, however, including the buildup of bacteria and mold or damage to the subfloor. 

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