Right around 1992, they were fazing in 1.6 toilets.
There were still some 3.5's being used.
The 3.5 drained the entire tank, which when refilled could sweat.
Does your current toilet, drain the entire tank?
The newer 1.6 toilets, only use some of the water in the tank, so unless you flush a couple of times, the water will not drop down so low.
Toto does make an insulated tank for the Drake if needed.
I've sold a few.
ST743SD