Black and gray tank connections

[Benbill]

I have a 2020 Montana 3931FB and I want to find out more about how the black and gray tanks work. Are the two black tanks connected to one another or are they separate? If they are connected, are they designed as one tank fills up it overflows into the second tank?

On the tank flush in the water house does it spray water into both black tanks? My black tank number two does not register any tank volume on the command console.

Thank you in advance for your knowledge and assistance.

Ben

[JRTJH]

To the best of my knowledge, NO black tanks are "interconnected"... It would be "impossible" to get the solid waste to flow between tanks or to "empty without the rush of water as the tank empties"... So, each tank will have a separate 3" dump valve. The tanks "may" empty through a common sewer connection on the side of the trailer, but each tank will be controlled separately...

Also, I don't know of any trailer with the black tank rinse system connected to both tanks so they are rinsed together.... To do so would overfill one tank while rinsing the other (or require both dump valves to be open during all rinsing operations)... If there are two separate sewer connections on the trailer (for two sewer hoses) it would make it "almost impossible to rinse tanks" at most dump stations without installing a complicated sewer hose system for a simple tank dump....

If your second black tank does not register on the control panel, and ALL the lights remain off when the button is pushed for that tank, I'd suspect the ground wire at the tank is loose, damaged or cut.

The way your system "should be plumbed" is with separate black tank valves, separate black tank flush connections and "possibly" a single sewer outlet for all black/gray tanks" Typically, the "main tank valves" are in the convenience center and the second bath valves may or may not be located in that same convenience center. Some are, some are installed closer to the tanks to prevent excessively long Bowden cable runs.

[Benbill]

Thank you for answering all my questions. What you say makes total sense. One my unit the tanks are all connected to a single drain line.

I only see one flush fitting for the main tank. Why wouldn’t they also provide a second flush? So frustrating. I had to run a hose up into the half bath. Not convenient and a risk of having a spill.

[JRTJH]

You can buy an "add on black tank flush kit" at any RV dealership and install it in any tank you want to have the capability to flush it "remotely". The kits are about $20-30 or so and fairly easy to install.

https://www.amazon.com/Camco-40123-Quickie-Flush-Preventer/dp/B000EDOSME/ref=sr_1_12?dchild=1&keywords=black+tank+flush+kit&qid=1598624550&sr=8-12

[rbrdriver]

If you do have 2 separate black tanks each one should have its on individual tank flush-out connection available. I know our Alpine does. It would be weird if it came from the factory and only one tank had a flush-out connection.

[Benbill]

I agree there should be one for each tank, but only one connector in the water room.

[Benbill]

That looks like a great add-on. I’ll need to look into that. Thank you.