oh, that sure does sound like a poorly thought out choice of tanks for that floor plan.
I'm sure that water helps, and of course one needs to use enough water anytime with solid waste, but shouldn't have to use an excess that will fill up the tank sooner!
Is it a straight shot down to the tank, so that you can see the ledge, so that you can see exactly what is going on?
Just brainstorming.... but I'm thinking of a flush nozzle placed at the ledge to deflect things a bit when you flush.
or maybe better
a wedge to turn the flat ledge into a poop slide.
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