Combining grey and black water tank

[Choper101]

Just finished interesting article, taking black water and draining direct to grey water tank (30 gallons). seems more manufacturer's are actually now building new rv's with combined grey/black tank for the boon docker campers. In all of my past travel trailers I found controlling my grey water usage was a piece of cake. So why couldn't one remove the stock toilet instsall in it's place regular rv toilet connecting waist line directly to grey tank?

[Shane826]

Black tank on TMs is an issue due to venting and due to space under the camper.

And I’m gonna need a link or something about these campers with all in one tanks.

[Bill]

RVIA does not seem to have a requirement for separate tanks. But several years ago, there was a move to require separate drains for black and gray tanks on RVs. I suspect that the push originated when new rules for wastewater treatment came into effect. Rural campgrounds, with no connection to city sewers, realized that treating gray water was a lot less expensive than treating black water, so if they could keep them separate, it would benefit them. It is also possible that filtered gray water could be used for certain purposes with little or no treatment - think golf courses, crop watering, car and truck washing, and so forth. A number of trailers, including a few TMs, were built with separate outlets.

The push for separate RV drains didn't last, but it did happen at about the same time as the formaldehyde scare, so they were possibly related.

Bill

[Kidkraz]

I used Google and there's a few sites that discuss combining these tanks, but I've not seen any specific RV manufacturer mentioned.
Interesting idea, when ya dump, both tanks go to the same underground tank.


https://rvblogger.com/blog/combine-r...ay-water-tank/

[Wavery]

I have actually thought of doing that. However, I would never do it with the existing grey water tank because they have issues with cracking open.

The other issue is, how do you plumb the toilet discharge pipe into the grey water tank with the frame in the way?

[commodor47]

Another consideration, although it probably does not apply to many campgrounds, is the ability to dump gray water but not black water. As an example, Borne Scenic Park, along the Cape Cod Canal, has some electric and water sites that allows one to dump gray water using a drain cap with a 3/4 inch hose fitting. The other end of the hose just fits into the gray water dump. Check out "Camping at Borne Scenic Park" in this link: https://bournescenicpark.com/about-u...ities/camping/

Dick

[donsev]

Smaller travel trailers like the Airstream Basecamp 16 and the 16RB Bambi and Caravel have a combination black/gray tank.

https://www.airstream.com/blog/under...20water%20tank.

From Basecamp Owners Manual:
Black/Gray Water Tank and Draining
To empty the combination tank, attach the sewer hose
by pressing the bayonet fitting onto the dump valve
outlet and rotating clockwise until it feels solid and
secure

[Larryjb]

The grey water is also used to clean out the black water from the discharge outlet and hose. If you combine the two, the discharge outlet, and especially the hose, will get very nasty smelling!

[chmartin]

This would sure make replacing the toilet easier. I'm surprised Trail Manor is not building the new models this way. Seems like an easy way to connect the two would be to tie the black water discharge pipe to the grey water discharge pipe. I'd use a T with a 45 instead of a 90 so that the water from the toilet flows towards the tank to hopefully keep it from clogging there. Would probably need a cutoff or flapper to keep the water from back flowing towards the toilet when emptying the gray water tank.

[LoveToCamp]

LarryJB gives the best reason (to me) of why not to combine both into one tank - most RVers use the grey water to flush the hose system after dumping the black tank. If all combined, that part of the flush is not possible. If there is no rinse water available at the dump station (I have found about half of the dump stations we have used don't have flush water available), then in order to flush-to-cleanse, one would have to go inside the trailer and run their water pump to put more fresh water into the combined tank, and hope you had enough fresh water available to do a good flush of the tank.

Regarding the RVs being made with combined tanks, all that I have seen have the bathroom sink, and sometimes the shower, going into the black tank, due to tank placement, or balancing of water discharge. They all have another grey tank that takes the kitchen drain, and most take the shower drain. This way, there is always plenty of water in the black tank to dissolve the solids. I have not seen any RVs that only have one tank for both black and grey, combined.