Walmart - I knew I had seen those containers but couldn't remember where.
I had been looking online at portable sinks like this - http://www.lowes.com/pd_356714-25344-PS ... Id=3578828
These things start at over $1,000 and go to more than $2,500.
They add in a 110v water heater (probably instant) but anyone with DIY skills can make one for way less.
Portable sinks and Porta Potti's aren't for every situation but they demonstrate the DIY route to a camper van can be had relatively easily and inexpensively.