This (wall mounted) tank is leaking at the large rubber washer that should seal between the flapper hardware and the bottom of the tank. The puzzle is how to access and replace the large rubber washer. The pipe connecting the toilet bowl and tank is hidden by a white ceramic pipe (apparently for cosmetic purposes) - and my impression is there's a smaller pipe nested inside the outer pipe. Because of the pipe I don't see how to access the large nuts securing the top and bottom ends of the down pipe (to the flapper hardware at the top end, and to the spud at the lower end). Channel-lock pliers aren't working there. There isn't enough space for a plumber's wrench. Can you suggest a good way to access the nuts without smashing the ceramic pipe? Somebody got the ceramic pipe(s) on! P.S. What is the function of the tabbed-nut between the two thicker nuts visible in the close-up photo?