All two-piece toilets have bolts that connect the toilet tank to the toilet bowl. If the tank is disturbed, such as a person leans back and slightly moves the tank (or cleaning or painting around a tank) a slow drip may occur. It can be very slight, sometimes not noticed for weeks.
Originally toilet tanks were secured to the bowl w/only one nut which is normally not a problem, however, over the years the bolt process has been improved by using a nut at the bottom of the tank to secure and make the bolt waterproof to the tank before it is assembled to the bowl.
A common mistake, and that is why I made this video, is that it’s common for a mechanic/handyman to put a metal washer under the head of a bolt, however in this case only a rubber washer is supposed to go against the head of the bolt so that when it’s tightened it will be; the metal head of the screw, a rubber gasket and then the china of the tank. The combination when tightened makes an easy waterproof seal.
With a new tank-bolt kit you’ll have (2 or 3 sets depending on how many bolts you toilet uses. Mansfield, older American Standard and a few others use 3 bolts). Take the brass bolt, slide on the rubber washer, insert it into the tank, (now you are on the outside/bottom of the tank) slide on the metal washer followed by the hex nut and snug up the nut. Now slide the bolt back and forth to center the bolt in the hole and tighten. It needs to be snug but not so tight as to crack the tank. I use only 2 fingers on the wrench and snug until I see the inside rubber washer ‘pucker’ a little bit.
Now the tank is water tight and is easily assembled to the bowl.