I don't know if there is a back flow preventer. I don't know what one looks like. If it is located in the white box it may be difficult to get into. There are 2 places to hook up hoses and one valve coming out of the box face. One for city water, one for the auto cleanout spray for the black tank and one that is just like an outside spigot to get water from the tank when outside.
I called A/S and spoke to Randy Mcneeley and asked him, but he was no help.
He said that water should not be dripping out, but he did not offer a way to solve the problem.
He sent me a plumbing diagram but that was no help and does not show a back flow preventer. Could the backflo preventer be in the pump itself?