How to stop your toilet tank from sweating - cutting styrofoam pattern to place in tank

How to Stop Your Toilet Tank from Sweating (With Styrofoam!)

Most people have run across a toilet tank that sweats. But why does this happen and how can you stop your toilet tank from sweating?

That’s what we’re going to learn with this fun craft project that solves your problem.

Why Would a Toilet Tank Sweat?

Condensation (or sweating) often forms on the outside of toilet tanks when air humidity is high. In other words, the inside of the tank is significantly cooler than the outside of the tank.

Occasional sweating is normal. However, continuous condensation may run down the side of the toilet and rot the floor underneath.

Preventing tank condensation requires insulating the inside of your tank. And that’s what we’re going to show you how to do with this DIY remedy for a sweating toilet tank.

Here’s What You’ll Need

To complete this homemade project, you’ll need the following items:

  • Kraft paper
  • Common pins
  • 1/2-0inch molded polystyrene foam (commonly called Styrofoam insulation)
  • Waterproof mastic
  • Sponge
  • Scrub pad
  • Utility knife
  • Putty knife

Stop Your Toilet Tank from Sweating in 7 Steps!

Now that you’re prepared with tools and materials for your homemade solution, let’s get started with the instructions. Follow them as closely as you can.

1. Turn Off Water Supply

First, shut off the water supply valve located under the toilet tank. It will be against the wall. Now remove the remaining water from your toilet tank with a sponge. You can squeeze out the water into your tub or sink.

2. Scrub the Inside Walls

Once you’ve removed all the water, you now must clean and dry the inside walls of the toilet tank. Do this with your scrub pad, then rinse the tank out. Let it dry completely overnight.

3. Make Front & Back Wall Patterns

Now it’s time to craft toilet wall patterns (or templates) using kraft paper. First, trim the kraft paper. You will need to create patterns for the front and rear inside walls of the tank. Make sure you trim the paper to a close fit. Cut out an area for the tank handle.

4. Cut the Foam

Pin the patterns you’ve just created onto the 1/2-inch Styrofoam insulation. Cut the Styrofoam to the shape of the paper with a utility knife. Then split the front panel vertically to fit the panel behind the handle.

5. Apply Mastic to Foam Panels

With a putty knife, apply waterproof mastic to the foam panels. Press them against the inside walls of the tank.

6. Make the Side Panels

You’ve already made the front and rear panels and placed them into the tank. Now it’s time to create the panels for the sidewalls of the tank. Use the same system as before for making these side-piece patterns, pin them to the foam, and cut the foam to shape.

7. Adjust, Fit, Apply & Wait

It’s time to fit and adjust your left and right-side panels. Once they fit as you’d like them to, apply mastic to the side pieces. Then press them into place inside the tank. Finally, let the mastic dry overnight before turning the water supply valve back on.

Alternative Remedy for Toilet Tank Sweating

Not everyone wants to go through the homemade process of crafting Styrofoam walls to place inside their tank. For those who like to DIY but want something more ready-made, try the Kenney K836-22 Anti-Condensation Toilet Tank Liner Insulation Kit.

how to stop your toilet tank from sweating - Kenney insultation kit being used to line inner wall of toilet tank
This pre-made insulation kit by Kenney prevents toilet tank condensation and comes with everything you need to insulate your tank.


Here are some great resources related to toilet repairs that you can do yourself.

Final Thoughts

Stopping your toilet tank from sweating isn’t your typical plumbing job. But it is important to take care of before it causes water damage to your floors or underneath your toilet.

The best part is that this homemade solution is a fun craft project that anyone can do without a plumber.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need toilet repair, replacement, or installation. 

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

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