Wastewater tank leaking?

[Raul Cortez]

We are currently living in our coach away from home. This weekend we left our coach for a three day trip back home. We arrived back at our coach today Tuesday, and we noticed a "smell" on the outide of the coach. The inside was normal. I looked around the coach and noticed water dripping from the tankage compartment hole plug. I openned the bay door and discovered the "smell" was "black" water in the tankage compartment? I looked through both sides but could not see the source of the leak? Does anyone have any ideas on where to begin to look? And how to locate where the leak may be? The reason I say "black" water is because presently I have the main dump valve closed, and the pneumatic valve open. I believe this enables all "grey" water to exit directly to the sewer line, and keeps only the "black" water in the tank. I have already emptied the tank just in case I was getting a false reading on my display. How do I find the leak if indeed it is a leak?