Transferring from one Gray Tank to Another

[BobKilmer]

My 381M has three waste water tanks:
- A 52 gallon black tank for the main toilet.
- A 52 gallon gray tank for the kitchen and main bath (I will call this the main gray tank)
- A 52 gallon gray/black tank for the half bath. (I will call this the secondary gray tank)
This gives me 156 gallons of waste storage, which matches well with the 155 gallons of fresh water capacity.

When boondocking the main gray tank is always the first to fill up. Meanwhile, the secondary gray tank doesn't fill nearly as quickly for our use. Has anyone else experienced this and come up with an easy way to transfer waste water from the main gray tank to the secondary gray tank? I have seen posts where people have done this with multiple gray tanks, but not with a gray tank and a black/gray tank.

My first approach to do this would be to interconnect the two tanks, but I would need to make sure that water only flows from the main gray tank to the secondary tank, not the other way since the main gray tank does not have a rinse feature. Home Depot has a DWV backwater valve that looks like it may do the trick:

https://www.homedepot.com/p/Oatey-Oa...9042/100144734

I haven't checked the plumbing line routing yet, but I suspect I would also need to install another check valve so I can open both gray tanks and let the fluids equalize without having the fluid come out the exterior drain. I am hoping something like this would do the trick:

https://www.amazon.com/Valterra-T58-...gateway&sr=8-3

Any other suggestions on how to do this or feedback from people who have tried something similar would be greatly appreciated. Thank you.

Bob

P.S. I know there are other solutions to my problem that require no work like minimizing the water usage, but I am hoping to keep my nice showers for another few days while boondocking

[Unlimitedmatt]

I think it would be possible with just adding the Valterra valve at the main outlet. When you want to equalize the 2 gray tanks, shut the new valve and open the 2 gray valves. You would need to be sure to shut the 2 factory gray tank valves first before dumping the black tank so you have the gray tanks available to drain after you dump the black tank and to make sure the black doesn't back up into the gray tanks.

[traveldawg]

Bob,
This has been covered before. You may find some info by searching some older threads. My comment would be this should work assuming both tanks are mounted at the same level.

Here is another thread about this just started today: https://www.mygrandrv.com/forum/show...255#post301255

Here is another that has been active for a while... https://www.mygrandrv.com/forum/show...376#post281376

And one more.... https://www.mygrandrv.com/forum/show...268#post279268

[DarylB]

I have the same situation, so far we've never even used the secondary black/gray tank for the 1/2 bath.
I was thinking it would be great if I could somehow plumb the kitchen sink to drain into the rear waste tank.

[BobKilmer]

Thank you for the feedback on the other posts. My question is a little different than the others, as I would actually be connecting a gray tank with a black/gray tank. That is why I was asking if anyone has tried that and used something similar to the backwater valve. I don't want the black/gray tank to backfill into the gray tank.