do not use metal washers in the tank, use only rubber washers, I retired from plumbing work & I guarantee that if you have a metal washer in the tank it will leak, best way to do this use a bolt & rubber washer inside the tank, use a metal washer & nut on the bottom of the tank well tightened, attaché tank to bowl with a metal washer & nut , tightened while applying pressure down on the tank, these do not need to be ungodly tight
I install toilets all the time in my business. This is the way to do it. Listen to the retired plumber.
