Need some advice on tank configuration

[Iceni John]

Anyone have any recommendations on what type or brand of pump to use to get the grey water into the black tank?

I have a small Harbor Fright "utility pump", about $30 on sale, mounted vertically so its impeller is always submerged (VERY important, if the impeller runs dry it will wear out in seconds), and it moves gray water from a dedicated 3/4" outlet about an inch off the bottom of the gray tank (so it won't suck nasties into it that may be lurking on the bottom of the tank).   It pumps the gray water to an inlet directly above the poo tank's main dump outlet, so if I get stalagmites or the Dreaded Mound Of Death blocking the dump valve it should help clear them.   If that doesn't work, I can also jet higher-pressure city water in through the same inlet, obviously with check valves on the city water and gray water feeds to prevent cross-contamination.

My poo tank is about 25" high, so if I wait until it's full before dumping I should get a vigorous flow of caca through the slinky.   I'm always amazed that the flat poo tanks in most RVs don't have more problems than they do with blockages and slow flow  -  they're just a poor design, but lack of space precludes anything better.

See, this forum has reverted yet again to discussing bodily waste.   "It's not an obsession, we're just busnuts."

John

[Brian Diehl]

... the shower and sinks will all have proper (domestic) water traps on their drains, which I would think would prevent any fumes getting past, but I'd hate to find that they didn't. ...

Jeremy,

I had a standard residential trap on my shower.  It was not deep enough to prevent fumes from coming into the bus if I had the front window(s) open.  The amount of vacuum created by the open windows at highway speed caused the trap water column height to be insufficient.  I had to cut out the trap and plumb in additional riser height on both sides of the trap so that I ended up with about 3" of water column height on both sides of the trap.  This stopped my fume problem.

Brian

[Len Silva]

In some motorhomes with two tanks, the bathroom sink is plumbed into the black tank to add a bit more water to it.

[BRUISER]

I have 2 tanks in mine.. 1 black and 1 grey.. we always fill the grey first and never have come close to filling the black.. I am currently looking into options to pump water from grey into black to extend my dry camping time with out filling up..

2 times now we have fill the grey to the point I was in shower and shower stopped draining

no more showers till I dumped..and black tank was almost empty..