How to fix a moaning toilet

More pooing, less booing.

If you’re reading this, it’s likely because there’s a loud moan shaking the floors or walls of your home. Maybe you’d describe it as a foghorn sound. Dragging chains, perhaps? No need to call a priest or paranormal investigator, though—it’s probably just your toilet.

There’s one good way to find out if the haunting sounds of stress and despair are coming from your toilet: flush it. Before you do, though, take the lid off the tank so you can look inside. There, partially submerged at the water’s surface, you’ll see an entity that can take many forms: maybe it’s a rubber ball on a horizontal stick, maybe it’s a plastic cup on a vertical pipe. It’s known as the float valve, fill valve, ballcock, or fill cup, to list a few of its many names.

When you flush, watch this valve. It’ll drop with the water level, then start floating back up as the tank refills. If you hear the moaning, rattling sound, gently grasp the ball or cup and lift it up until it can’t go any higher. If the sound doesn’t stop, you might have water pressure issues or some other problem that’s beyond the scope of this article. If things go quiet, the valve is to blame—and we can help.

Why is my toilet yelling at me?

In short, the fill valve isn’t closing properly. When the float lifts, it’s supposed to stop the flow of water into the tank and has to fight against the water pressure inside your pipes to do so. Over time, it wears down. It’s similar to trying to plug the end of a running garden hose with your thumb, says Ash Hicks, of toilet part manufacturer Fluidmaster. Eventually, your thumb will get tired, the seal will break down, and water will start spraying out the sides. That’s what’s happening to your toilet. It’s not necessarily leaking—it’s struggling to close.

How to fix a broken fill valve

Toilets don’t have many moving parts, so they’re a relatively simple DIY fix. Still, if you’re not careful, you can crack the tank or damage the water supply line. If you feel like you’re in too deep at any point, there’s no shame in calling a plumber.

But if you’re doing it yourself, find the pipe going into the wall behind the toilet and turn the valve clockwise to shut off the water supply. This will ensure you don’t get wet while you work. If it’s stuck due to rust or mineral buildup from hard water, spray it with a bit of WD-40 or lightly tap it with a pair of adjustable, groove-joint pliers. Don’t hit it too hard, though—if you break this valve, you’ll have to rush to find the main water shutoff for your home while your bathroom floods.

[Related: How to figure out what’s wrong with your toilet]

Now, it’s time to replace the faulty valve. Although the issue is likely just one worn-out washer, we recommend installing a whole new fill valve. It’s easier because most hardware stores sell complete replacements and the repair will last longer. You can even buy a kit to swap out everything inside your tank if you want to give the commode a bit of a refurb. 

Use a pencil to mark the water level inside the full tank, then flush the toilet. Most of the water will drain out, and since the water supply is off, it won’t fill back up. Take the refill tube out of the overflow tube—this is the other vertical pipe in the tank, and the one that refills the bowl after you flush.

You can remove the remaining water with a shop vacuum, sponges, or towels, or just leave it there until the next step.

Find where the water supply line connects to the bottom of the toilet tank and put some towels or an empty plastic container on the floor underneath it. If you left water in the tank, whatever you use should be big enough to hold all of it.

Unscrew the nut that links the supply line to your toilet. It shouldn’t be too tight, but you might need pliers. Then, remove the nut that locks the fill valve to the tank. Take out the valve. You may be able to remove and replace just the top part of the valve without unscrewing these nuts, but because stores sell complete valves, it’s rare that this will be the best course of action.

When you slide the new valve into place, make sure it’s set at the correct height. There should be a “critical level” (CL) marking near the top of the valve, and this should be about an inch above the top of the overflow tube to prevent any toilet backflow into the public water supply. If it’s not, you’ll have to take it out and increase the valve height. On newer fill cup valves, this just means turning it counterclockwise.

When it’s at the right height, put the refill tube back into the overflow tube and fasten your new valve in place. Be extra careful when you tighten this nut and reattach the water supply line, because overtightening can crack the tank. Tighten the water supply line with your hand, then give it a quarter turn with the pliers to ensure it won’t leak.

Turn the water supply back on and let the tank fill, checking for any leaks. Ideally, the final water level should match the line you drew at the start, or end up no less than an inch below the top of the overflow tube. If it’s too low or too high, you’ll have to adjust the position of the float. The fill valve you bought should have instructions for how to raise or lower your particular model.

With any luck, you’ll have exorcised your plumbing demons, at least for several more years.

John Kennedy

John Kennedyis PopSci's DIY editor. He previously covered legal news for Law360 and, before that, local news at the Journal Inquirer in Connecticut. He has also built and remodeled houses, worked as a fencing coach, and shelved books at a library. When he's not taking things apart or putting them back together, he's playing sports, cooking, baking, or immersed in a video game. Contact the author here.