I use two 5 gal non pressurized SS Beer/soda kegs, no grey water, it goes out a hose in the floor onto the ground or into a small plastic bucket that just fits under the van (depending where I am)
its out now for winter but I'll see if I have a photo somewhere
Found a photo
A new photo with the pump removed for winter
I now have two SS fresh water tanks instead of the one in the photo. The pump basically sucks the water from whatever tank the hose is connected to them pushes it to the faucet thru both the hot & cold for simplification. If I had a hot water heater I would need another pump and have to separate the lines, of course. The pump is on demand and only comes on when the valve (faucet) is opened.
I have 2 6 gallon water jugs and a 3 gal gray water, a flo-jet pump and a shurflo accumulator tank. There's a flex hose which I can move from one jug to the other.