BLACK TANK OVER FLOWS INTO BATHROOM SINK

[MikeLoriCross]

Here is one for y'all...

We have a 2021 Milestone 379FLML. We have a half bath that has it's own black tank and shares the gray tank with the kitchen sink. So for clarification, the half bath toilet has it's own black tank and the sink shares the gray tank with the kitchen sink and the washer.
recently the half bath black tank has been filling with water and overflowing into the half bath sink. Last night we found it full with laundry water.

* NO PLUMBIMG, HOSE, VALVES, etc. have been touched. we have lived full time in it for 9 months, stationary for the most part and hooked up. we have been in our current spot 3 months and LAST WEEK THIS STARTED. We are able to let the gray drain so those valves are always open, the black, and i've dumped those prior to this, we use portable tanks which I dump about every week and a half.

I have looked at what diagrams i can find for this, most are very generic and no help. As far as i can tell there are no connections between those two systems other than the vent(s) piping.

I would like to see a complete plumbing diagram for this specific model or if someone out there has had this problem, point me to a possible reason.

 

[Bogie]

Try contacting Hearland customer service. Have your VIN number ready. They should have a diagram for this and should be able to email it to you. I had them send me the diagram of the frame on my Sundance. They were very accomomdating.

 

[danemayer]

recently the half bath black tank has been filling with water and overflowing into the half bath sink. Last night we found it full with laundry water.

Why do you think that the water in the sink is coming from the black tank? The more obvious cause would be that the shared gray tank is full.

 

[JohnDar]

According to the literature, you have a single 80 gallon gray tank and a single 80 gallon black tank. It would be my guess that the two toilets share the black tank while the washer, shower, kitchen and two lavatory sinks share the gray tank. So either the single gray tank is full and you're using more water than you estimate, or there is an obstruction preventing it from draining completely. Possible that there is something blocking the half-bath sink drain, as well.