Think summertime. Sitting outdoors on a hot humid day with a nice cold beverage. The cold beverage within the glass causes condensate to form on the outside of the glass. The condensate runs down the glass and puddles on the table top. In your bathroom, toilets are typically filled from the cold water supply line. Cold water goes into the tank, chills the porcelain, and if the relative humidity in the house is high enough, condensate can form on the outside of the tank, run down the tank, and pool on the bathroom floor. If you have air conditioning, running the AC dehumidifies a house, making condensate less likely to form on a toilet tank. But a nutshell answer as to when an insulated tank would be recommended? If you have condensate forming on the toilet tank, then an insulated tank might be a good idea.

Use Sikaflex,it is used all the time with boats for below the waterline.

There are a few different versions of the gasket( fat and soft,thin and soft,fat and firm,thin and firm) although you will only frind one or two at big box stores. Like so most things, experience shows if gasket is correct when tank rests on bowl with the right gap before tightening bolts. Big box gaskets are usually very soft and thicker than nessary. If over compressed,the gasket is squeezed from between coupling. Assuming that's what's happening,try shimming between tank and bowl. The shim material needs to be about 3/8ths thick -- + ,flat and about the consistancy of the rubber washer on flush valve you replaced earlier. The preferred consistancy is one which you can only slightly compress between thumb and index finger. Evenly shim all four corners and do not over tighten bolts. Just snug enough tank can only be rocked fore and aft 1/2 inch with one finger,not rock at all side to side with any less force than applied with palms pressing on top of tank. If there is more than 1/4tr inch between tank lid and wall,shim there also to prevent leaning back and rocking tank eccessivly. On the other hand if tank is tight against wall (unable to create gap with pressure of one finger) it may be cock-eyed at coupling which makes over/under tightening even more unforgiving. Idealy there is a gap between wall and tank but little or none between lid and wall, Only if you ask,I'll tell you why cussing helps.

I love them.....the ones I bought were mainly a chlorine compound and definitely made the bowl stay cleaner....and less germy. But the bathroom smells rather like a swimming pool! However they do cause metal parts of your toilet to corrode after a few years of use. You still have to use a brush every couple of weeks and need to be careful not to use traditional toilet cleaner when you use the chlorine compound or you release a dangerous amount of chlorine fumes.....but your bowl will be cleaner....just as if you poured some Chlorine bleach into the bowl after every flush.