I believe what Jon is saying is that his toilet ,for the fresh water supply, has no check valve, so if the flush valve fails and you can not stop the water from flowing thru the toilet, you will have back flow from the toilet the minute you turn off the water pump or city water. The back flow from the toilet would drain back towrds your pump and fresh water tank.
This would be a worse case scenario depending upon how your cold water pipe is plumbed from the toilet back toward the pump and tank. If there were T's in the line, and or wheter the toilet cold water pipe was plumbed vertically up the back wall high enough to create an air space.
My question would be ' what was Liberty's opinion on this?' Gary