Our powder room toilet drain was installed 1/2" too close to the back wall. The top of the tank hits the drywall preventing it from sitting level on the bowl. The rubber gasket between the tank & bowl, apparently doesn't compress enough in the back & it leaks. Shy of relocating the drain further from the wall, any suggestions? Thanks

" Shy of relocating the drain further from the wall, any suggestions?"

Short of recessing the drywall your only option would be to install a offset flange. Good luck, Tom