Transferring Gray Water to Black Tank

[BoscoMN]

Hi folks,
If I can make it fit I will be installing a composting toilet into our 2015 19' Flying Cloud. My question is about how best to utilize the Black Water Tank as a secondary Gray Water Tank. I am thinking of using a termination cap with a hose fitting mounted on the common dump pipe. A hose would go to a water pump that then connects to the Sewer Flush connection on the outside of the trailer.
1. Once the Gray Water tank was at 3/4 full (16 GAL) I would set up the system and open up the Gray Water valve.
2. Start the pump and fill the Black Water tank (16 Gal into the 18 Gal tank), making sure not to run the pump too long without water.
3. Shut the Gray Water tank value, drain the hoses, pump and residual gray water from the dump tube/termination cap into a bucket. Dump bucket where permitted.

I think I may make the hose going from the pump into the Sewer Flush connection a 3/8" flex tubing so that the pump could never pressurize the Black Tank or force water up into the plumbing vent pipes.

Discussion, ideas, thoughts are most appreciated!

[Aerowood]

Are the tanks both under the floor? If so put a fitting in the top of the gray tank and have it act as an overflow into the black, if the slack is on top of the floor then replumb the gray to the top of the black with an overflow to the grey. Let gravity work for you instead all of the extra pumps, valve, etc that can fail.

[BoscoMN]

Definitely something to consider - I always like the KISS principal.

The Black Tank sits above the floor and forms the pedestal that the gravity toilet dumps right into. The Gray Tank is lower that the Black tank. Without seeing any drawings, diagrams, articles or photos of this plumbing configuration ( I just bought the trailer and it is in storage until April) I am just guessing on most of it. But the shower drain is also lower than the Blackwater tank and there may be no easy way to reroute the sinks into the top of the Black Water Tank. Another thought in the back of my mind is that in 3/4 years I will retire and go on longer trips so we may move up to a larger Airstream. Then we can just replace the original toilet and the trailer would be back to factory configuration to appeal to a greater number of buyers.

[TG Twinkie]

I installed a 21 gallon tank above the floor in my Argosy. I use a pump to transfer from the original gray water tank to the 21 gallon tank. When both tanks are full I first empty the 12 gallon tank. Then open a ball valve to dump the 21 gallon tank. The 21 gallon tank empties into the 12 gallon then flows out the dump valve.
I would think you would need a very good filter to prevent the black water flush nozzles from plugging with the particles in the grey water.

[DaveFL]

3/4 camping seasons in Minnesota is less than a year of use but using the average usage of a camper, you probably are spinning your wheels, almost all campgrounds have dump stations and it takes less time to dump black than grey. Unless you are looking for a the plumbing experience

[Ted S.]

There was a video online called something like " insanely easy way to combine black and grey tanks " you would likely find helpful, should be easy to google

[Ted S.]

Here it is

https://m.youtube.com/watch?v=T1dXcBchbuQ

[BoscoMN]

TG Twinkie, thanks for the heads up about the spray nozzle - I had completely forgotten that it was on this line. I had seen the Wynns' video and thought that would work for my 19' Airstream but I believe that I would only be able to fill the black tank up to the level equal to the height of the shower stall floor drain (very little). Any more water in the combined tanks would eventually come out the shower stall and will not go into the upper part of the black tank.