How to Remove a Water Supply Coupling Nut

Date Posted:3 February 2022 

How to Remove a Water Supply Coupling Nut main image How to Remove a Water Supply Coupling Nut image

Having leaky toilet issues? We all know how much of a messy situation that is! Not only does the leak puddle cause moulds and mildew, which can be toxic to your health, but it can also lead to skyrocketing utility bills. It's a good thing toilet leaks are easy to repair. With just a standard tool, you'll have a neat and working toilet in no time!

What Are Coupling Nuts Used For?

Coupling nuts are used to join two male-thread bolts, rods or pipes. They come in a variety of sizes, materials and grades to suit the pressures of a job.

You’re most likely to encounter a coupling nut, also called an extension or hex coupling nut, on standard toilets, typically underneath the tank, where water comes in. The component provides a secure connection between the main water supply line and the toilet tank. Within a coupling nut, you'll find a rubber or synthetic washer that clamps down when tightened to ensure a watertight seal. A leak at the base of your toilet's water tank points to a problem with the coupling nut.

What You'll Need

  • A sponge or towel
  • A bucket
  • Locking pliers, an adjustable wrench, or a spud wrench

Steps to Remove a Coupling Nut

Removing a coupling nut from a toilet tank is simpler than it sounds. We've put together these easy-to-follow steps so you'll know exactly what to do and how to avoid mistakes. If your toilet has a plastic coupling nut bolt, make sure to be extra careful not to crack it — you don't want a flood in your bathroom.

#1: Close the Water Fill Valve

The first important step is to close the water fill valve that feeds your water tank. Do this by turning the knob clockwise until it stops. If the fill valve seems impossible to find, and you don't mind having no running water for a few minutes, then you can close your home's main water supply. This valve is typically located in the basement, garage or just outside your house.

#2: Place a Bucket or Towel Under the Toilet Tank

As an extra safety measure, even when the water supply is off, make sure to place a bucket underneath the toilet tank. This way, even if water spurts or leaks out, there won't be a mess.

#3: Drain the Water Tank

Take off the lid from your toilet tank and flush the toilet repeatedly until there's no more water left inside the tank.

If you still have water left in the tank, you can use a sponge or a towel to soak up as much water as you can and wring the water out in the bucket. You can also do this with a wet/dry vacuum if you have one.

#4: Remove the Coupling Nut

Once the tank is empty of water, look for the coupling nut located on the underside of the tank. Use a pair of locking pliers, adjustable wrench or spud wrench to loosen the nut. You can continue loosening the coupling nut with your fingers and gently pull the nut out.

The water supply line will then break loose from the connection, so make sure to place it in the bucket to catch the remaining water inside.


If the coupling nut is made of plastic, make sure to handle it with care; they're not as robust as stainless steel coupling nuts. Plastic plumbing parts are prone to stripping, cracking or breaking. To avoid this from happening, be careful not to overtighten when replacing the coupling nut.

Solutions for a Stuck Lock Nut

Sometimes it can take a bit more effort to unscrew a coupling nut. However, you want to be sure you don’t damage the nut or the pipes. You can try the following methods to deal with a stuck nut.

Apply Heat

You can try using a hairdryer, a hot cloth, or any other source of mild heat to lubricate and loosen the nut a little bit. Next, apply slight pressure on the nut while warming it up. You can then start unscrewing with pliers or a wrench.


Plumber's grease is one of the most efficient ways to loosen a difficult nut. First, lubricate the stuck nut with a plumber's grease and let it sit for 10–15 minutes. Then proceed to remove the nut with your pliers or wrench.

Clean the Buildup

You can use a calcium dissolver or a WD-40 to remove the calcium buildup and eliminate rust; this will help you get your nut unstuck. Ensure to read the instructions and wait the appropriate time before cleaning the buildup with a cloth.

Replace Your Coupling Nut

Now that you've taken off the coupling nut, you're ready to install the replacement. Head to ReFast to shop for a durable and efficient coupling nut supply and other fittings. Shop now!