you may want to run a closet auger into it a few times in case
something is clogged in it.,once had one that would flush water but not
solids, had a pencil stuck in it,once a toy. clean the holes under the
rim out with a nail or screw, make sure the vent pipe on roof is open by
running water into it with hose.

http://www.minibite.com/america/malone.htm