Gray water drainage design help (see drawing)

DutchmenSport wrote:
The holding tank under the sink will work just fine. But the tank the shower drains into will not. The tank will fill only as full as the height of the floor of your shower. That tank needs to be lower than your shower. If not, you'll have water standing in your shower.

A better option is to simply do away with the bilge pump idea and have 2 separate independent holding tanks with drains at each one. The tank still need to be UNDER the shower floor, unless you raise the shower floor.

I think you'll find the bilge pump idea will quickly be a PITA. Let gravity do what it does best, .... make water flow down hill.

You have room under the sink for a tank there, make room under the shower. Your toilet is a cassette port-a-potty style, so nothing to extra plumb there. It's self contained.

About dumping that water on the ground ... um ... you really need to rethink that.

Well here's how I planned it, I have to build my shower pan out of fiberglass, it's pretty tight in there, right now the free space is 32"Wide x 24"Deep x 72.5"High, I have to make a slope towards the drain, I planned that the lowest point in the shower floor would be 2.5" higher than the bottom of the bilge pump pan, and the pump would automatically start when about 1.5" of water is in there, so theoretically the shower pan would always drain.

I can't raise the pan to add a tank underneath I don't have enough head space for that, so I would have to add it under the van, exposed to the cold and freezing weather...

Please give me more detail why the pump idea would be a "PITA" like you say, I simply want to understand why.