It never occurred to me, why not just one tank?

[Pslif]

Just sitting here pondering the facts of life. On my trailer there is a black tank in a gray tank, just wondering why can’t there just be one time for all your waste ?
I do understand that if you empty your black tank first and then the gray it should leave it “ particle free” . But why not just use one tank and then flush it with the tank flush?

[lenny-shawna]

Originally Posted by Pslif

Just sitting here pondering the facts of life. On my trailer there is a black tank in a gray tank, just wondering why can’t there just be one time for all your waste ?
I do understand that if you empty your black tank first and then the gray it should leave it “ particle free” . But why not just use one tank and then flush it with the tank flush?

I believe Newell uses just one tank, but then again, those rigs are north of 2 mil. As for the others, well, maybe it has something to do with weight distribution.

[georgelesley]

An American Cruiser class B we had years ago only had one tank

[EdInArk]

I don't know if it's a consideration for the manufacturer, but some COE parks allow grey water to be dumped onto the ground, but obviously not black. You'd need separate tanks there.

[Argosy]

Weight distribution, size, tank weight, and cost. There's a lot to fit in/under an RV, two smaller tanks are easier to fit than one large one. Costs go up fast when a tank gets larger, the manufacturing equipment is larger, the walls have to be thicker, production time is longer per piece.

[Soppy]

My gray and black tanks sit side by side in the same compartment. They could have easily installed one larger tank in the same space.

[sgl22150]

I might be able to give some insight. I started camping with my parents in 1954. I have grown up with camping and have worked on campers both for hire and repairing my own since 1964 at the age of 14. Most of the earlier , if not all of the earlier campers only had one holding tank- black water only. There was no gray water tank. It was accepted to let gray water run on ground. A lot of those units only had a kitchen sink to generate gray water, Even into the early 70's gray water tanks were not installed on all units.

[Talloaks]

In the good old days, gray water was not considered a hazard and was often disposed of by digging a small "gopher hole" in the ground and running a short piece of garden hose into it. Or, you allowed it to drain into a bucket under/behind your rig, with a nail hole punched into the bottom. And people didn't generate as much gray water years ago as we all do now. So no provision was made to collect it in a tank.


I had a 1966 Airstream that was set up this way. One waste tank, for toilet waste only.


I don't know this to be a fact, but it is possible that the maintaining of separate gray and black tanks stems from the notion that gray water was environmentally benign and it was not necessary to dispose of it into a sanitary sewer system. Someone else may weigh in with a better explanation.

[Ljwt330]

This is a great thread, IMO, and I think it touches on the answer.

I believe having two separate tanks, or at least having a grey tank, is an evolutionary change brought about by the addition of facilities in rvs that use more grey water. As mentioned, earlier rvs did not have showers or vanities, and conserving water from the fresh tank for essential purposes was mandatory. Once larger rvs were built with large consumption fresh water devices, it became necessary to route the grey water somewhere, so tanks were installed. One or two tanks for both waste water sources became a design decision.

Add to this the rise of private RV parks/campgrounds and the closeness of sites in many state/local park campgrounds, and you can understand the need to restrict the dumping of grey water around campsites. Holding tanks for both waste sources became required in factory produced RVs so they could be marketed nationwide.

[Marine359]

Just a guess: Phosphates in detergents are bad for ground water, and surface water. For many years it wasn’t possible to buy phosphate free detergents. Today you can, so your gray water can be benign. But not everybody uses phosphate free.

[shootist]

Grey water is legal to discharge on the ground in many states. As long as the kitchen sink is not connected to it. Goo in the blackwater tank and soap and dirt in the grey. Some new rvs have the kitchen sink dump in the black

[Persistent]

In most home sewage systems there is a 6 to 8 foot drop between things like lavatory and sewage outflow or holding tank. In an RV, there may be 4 feet and the sewage outflow is designed to be closed off.

Back up of black water can easily flow into sinks and showers when not operated correctly. Two tanks prevents dangerous black water from getting into sinks and showers where it could contaminate food, water, and people.

[MSHappyCampers]

Originally Posted by Persistent

In most home sewage systems there is a 6 to 8 foot drop between things like lavatory and sewage outflow or holding tank. In an RV, there may be 4 feet and the sewage outflow is designed to be closed off.

Back up of black water can easily flow into sinks and showers when not operated correctly. Two tanks prevents dangerous black water from getting into sinks and showers where it could contaminate food, water, and people.

I'll buy that!

[Jay D.]

Originally Posted by shootist

Grey water is legal to discharge on the ground in many states. As long as the kitchen sink is not connected to it. Goo in the blackwater tank and soap and dirt in the grey. Some new rvs have the kitchen sink dump in the black

you don't dump gray water in OREGON. you will, might get a hefty fine. the DEQ considers gray water more of a hazard than your black water .
Jay D.