The macerator pump is located AFTER the bayonet valve. The 3" pipe from the bayonet valve then reduces down to about 1 or 1-1/2" before going to the macerator pump. I suspect that this is where my problem lies, but I have not taken anything apart yet because I don't want to have a nasty mess inside the compartment and ON ME when I open things up. Granted, the only amount of mess will be what's between the bayonet valve and the macerator pump, but still, I'd like a sanitary way to do this! Changing diapers on my kids was nearly enough to kill me, much less dealing with this kind of mess!