The inside diameter of that tubing I believe this 3/8" x 1/2 O.D. One
thing that has not been mentioned for portable showers, and just pumping
water in general is the Coleman hot water on demand system. I don't know
about the rest of you, but I don't wash dishes inside the van. The sink is
just too small, and too much water gets splashed around with tubs. The
Coleman hot water system is perfect for pumping cool water, or rotate the
knob little bit more and you have warm (100 degree water) or rotate the
knob a little bit more and you can get a scorching hot 160� water for tea
or whatever. If you were near a stream, you could actually heat up to 40
gallons of water on a single charge and bottle of propane. Now, that's
just cheating! It's a pretty slick little system, but I probably would not
spend the $200 or so they want for. I saw one on eBay for $90, and grabbed
it along with the sprayer. I love it.

One other thing worth mentioning. You could put a valve at the bottom of
the van in the drain cap of the holding tank. No pump needed, just let
gravity do the job. How's that for a solution?

Troy