nextlevel wrote:
I don't keep water in the gray water tanks being that I am hooked up to a septic tank.
Since it only happens when the black tank is nearly full, this isn't your problem, this time. However, be sure you have put a "U" shaped trap in your dump hose to hold water to keep the septic tank smells from coming back into your gray tank, and possibly into your trailer. It also keeps insects that may be living in the septic system from infesting your gray tank. (The insects are a problem in sewer systems, I don't know about septic systems.)