I have a rear exit toile that has just started giving me a flushing issue. It acts as though it is partially stopped up and doesn't flush all the way. I have plunged, snaked and even removed it and shot water through it. There doesn't seem to be anything in there.

Take the tank lid off, flush and tell me what's happening. Does the tank refill to the right water level? Does the water in the bowl swirl when you flush? Does the water rise in the toilet bowl when you flush? What happens when you dump 3 good buckets of water in the toilet? This is a manual flushing.

Does the water go down slow in the toilet bowl?