How to Fix Condensation on a Toilet

Updated February 21, 2017

When it gets hot outside, the humidity inside rises. When that humidity hits your cold toilet tank, the moisture in the air condenses on your toilet tank and bowl. This happens because the water in the toilet is much cooler than the moisture in the air. The condensation can run down the toilet and eventually start to rot the floor. Adding a little bit of hot water to the toilet tank is a sure-fire way to stop toilet condensation.

Turn off the main water supply to the house via the water main. With the water off, turn on the hot and cold faucets in a sink to drain the water from the water lines.

Locate the cold water line that leads to your toilet. In many cases you must go to the basement to locate the copper line or you may have to remove part of your drywall.

Thread compression adaptors to each end of the three valves on the anti-sweat water valve.

Place the anti-sweat water valve over the horizontal water pipe approximately 1 inch away from where the pipe becomes vertical and goes up to the toilet. Mark the location where the middle valve meets the vertical copper pipe.

Place a T-fitting over the mark on the vertical pipe and mark the ends. Cut the section of pipe out with a hacksaw.

Coat the cut ends of the copper pipe and the ends of the T-fitting with pipe flux. Then, position the T-fitting between the cut pieces of pipe so the open end of the T-fitting runs parallel with the horizontal pipe. Solder the T-fitting into place with a blowtorch and pipe solder. To do this, heat the ends of the pipe with the blow torch and then hold the stick of solder against the pipe joint. As the solder melts, rotate the stick around the pipe to create a consistent seam.

Place pipe dope around the open tubes extending off the valve. Slide compression nuts onto each end of the open tubes.

Cut the section of horizontal cold water pipe so you can connect the bottom valve of the anti-sweat water valve into place. Place the valve into the cut section and solder it with the blow torch and solder.

Coat the open ends of the cut pipe with pipe dope and then place the anti-sweat valve between the cut pipes. Slide the compression nuts halfway over the cut pipes and half way over the tubes extending from the valve. Tighten the couplers in place with the wrench to secure the valve.

Secure the middle valve to the T-fitting you installed previously.

Locate the nearest hot water line and cut a section out for a T-fitting. Solder the T-fitting in place. Solder copper pipe to the T-fitting until you reach the top valve on the anti-sweat valve. Connect the copper pipe to the compression fitting on the valve.

Turn on the water main and check for leaks. If you locate any, turn off the water and solder the joints until the leaks are stopped.

Turn the valve on to add a small amount of hot water to the toilet tank to raise the temperature.

Things You'll Need

  • Hacksaw
  • Compression fittings
  • Anti-sweat water valve
  • T-fittings
  • Blowtorch
  • Solder
  • Flux
  • Pipe dope
  • Compression nuts
  • Wrench
  • Copper pipe
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