Toilet bowls sweat because the air around the toilet is considerably warmer than the temperature of the toilet water. This creates condensation and causes the toilet to sweat. You can purchase an anti-sweat toilet kit to insulate the tank and reduce condensation. The kits are inexpensive, easy to install, and are very effective. Liners are applied with an adhesive to the inside of the tank. They are nearly permanent, and will require some effort to remove.
http://www.elocalplumbers.com/content/plumbing-articles/why-is-my-toilet-sweating-3931
4. Install an anti-sweat valve in the toilet supply line to warm the water in the tank. The valve does this by mixing hot and cold water. To install one, trace the toilet supply pipe to a place where it runs near a hot water pipe supplying a sink, shower or bathtub. Turn off the water to both pipes.
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Step 2: If the water level is correct but there’s still not enough water coming from the tank to clean the bowl properly, the problem may be the tank ball on the flush valve seat the bottom of the tank. The ball is probably dropping too soon because the guide is set too low.
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Step 3: Look for other cause of inadequate flushing. The small ports around the underside of the toilet bowl’s rim can get clogged with residue from chemicals in the water and prevent a sufficient amount of tank water from running out into the bowl.
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Condensation on the outside of a toilet tank is the result of humid air in the room coming in contact with cold tank. This will happen on a glass filled with a cold drink. Condensation on toilet tank is most often a problem in the summer time in humid climates, but can also be a problem in the winter. In addition, houses on well water suffer a great deal from this problem. Houses built in the 70's are more air-tight and energy efficient, consequently humidity is easily trapped indoors.
http://helptopics.us.kohler.com/link/portal/5641/5712/Article/1141/What-Causes-Condensation-Outside-Of-A-Toilet-Tank
3. Install a tank liner. Shut off the water, drain the tank and let the inside of the tank dry out. Glue the liner to the inside of the tank with waterproof glue. The liner and glue usually come together as a kit.
http://homeguides.sfgate.com/stop-toilet-tank-condensation-39185.html
Condensation is worse in a poorly ventilated bathroom. Condensation on the outside of your toilet tank can lead to a host of problems, including mold, corrosion of metal parts and floor damage. It's caused by a temperature difference between the inside of the tank and the outside.
http://homeguides.sfgate.com/stop-toilet-tank-condensation-39185.html
Fed up with condensation dripping constantly from the bathroom toilet? We were! http://pixels1.com/stuff/how-to-stop-... So we insulated the toilet cistern using a tin of Expanding Foam!
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A constant exchange of fresh cold water in the tank will cause condensation to form on the outside of the tank when the humidity is high in the bathroom. Check the toilet for leaks.
http://helptopics.us.kohler.com/link/portal/5641/5712/Article/1141/What-Causes-Condensation-Outside-Of-A-Toilet-Tank
The wax ring seal that joins the bowl to the drain outlet may be defective. If this is the case, the bowl must be removed, and a new gasket installed. If the leak is due to a crack in the tank or bowl, the whole toilet must be replaced.
http://home.howstuffworks.com/home-improvement/plumbing/how-to-repair-a-toilet5.htm
what causes condensation on toilet bowl
The air around the toilet is considerably warmer than the temperature of the toilet water. This creates condensation and causes the toilet to sweat.