Mesakeca wrote:
I get what you mean about the vent and that was our first suspicion also but running the sinks with the drain open or closed makes no difference. Too bad , eh? I'll post later with the 'results' of tonight's trailer fixing event. Thanks again to all of you!
Sue
Actually, that is not "Too bad." It definitely points you at the pipes just before the tank and after the shower drain. That can't be a long stretch of pipe.
If you can, run the plumbing snake down the shower's drain into the gray tank. That SHOULD break up any blockage.