Originally Posted by yorkie_chris

That would depend where the pipe has rotted through.

Pop the tank off, blow into a pipe on the bottom of the drain (it's hidden underneath, just in front of the hinge). Put your finger on the top of it (next to the filler hole), you should be able to feel pressure. If no pressure, and the air you blow in is going into the tank, you haz this problem.

It would explain your running issues.