design question - possible two stage tank?

[type901]

We are building a 1969 21ft AS. I say building, because we are starting from scratch. We have decided to place the washroom in the roadside center of trailer, just to the left of the door. We purchased small (very small) toliet/shower basin, that has a built in black water tank. Pelland Enterprises Motor Home Products - RV Windows

I am concerned that the black water tank that I have is kinda small. Product specs don't say, but it cannot hold more than 4 gallons.

I am thinking of installing another black water tank in the floor, and connecting the first to the second for the added capacity. I could place the second tank within a foot of the first (maybe even right under it). Is this possible, or I am just asking for plug ups? Maybe if I install a valve at the first tank, that dumps to the second tank?

[terryV]

Well, a 4 gallon black water tank is way too small, unless you use your toilet only for emergencies. (I do have some friends who only use the campground toilet, unless they have a middle of the night emergency. Even then, no pooping in the camper.)

I would think it would be best to have a "real" tank directly under the little one with a straight drop thru into it. Being able to look down thru the toilet into the large tank would be best.

A valve between the two would probably be a good idea to help with the "stuff" that is going to hang up in the top tank.

[idroba]

The '73-'78 GMC motorhome with the front wheel drive Olds drive system had a combined 40 gal gray and black water tank. As an option, you could get the Thetford recirculating toilet which had a several gal capacity and used the filtered waste water to flush over and over. With enough chemicals, it worked fairly well.

The point is that when the Recirculating toilet became full and needed to be re charged, you pulled a dump valve lever in the toilet bottom, which dumped the contents into the main 40 gal tank. So, the concept has been used in the past with a slightly different system. The GMC motorhome that I owned did not have that recirculating toilet system to begin with, but the GMC Forums members who had it said it did extend their tank capacity a lot.

Airlines have (or used to have) recirculating toilets that work the same way. A charge of chemically treated water holds both the waste and is used for flushing over and over. A screen inside prevents the solids and paper from the flushing stream.

I think Thetford still makes the system, but it has never been very popular.

[terryV]

I've had that system in a Scotty trailer, and in several boats. It does work very well.

However, since I became old, (I'm not exactly sure when that happened) I have become somewhat of a toilet snob. I want my toilet handicap height, and I want it made of porcelain.

Yeah, I know, If I knew I was going to live this long, I would have taken better care on myself.