I recently replaced a wax ring on an old top tank toilet. The bowl sits about four feet lower than the upper tank, After running around town for hours I realized that the specific gasket that I needed was not being made (or not available). I made my own to connect the flush pipe from the tank to the bowl.
No leaks, flushes strong, great. Now it makes a loud groaning noise when it is flushing. Is this the gasket? A lot of parts got jostled and I would be surprised if I broke something this entire toilet was built before gravity according to the local shops.