I was just doing some research for my own little entourage and I thought you could get some mileage out of what I learned.
I just spoke with Mindy Cook over at United Site Services (775)826-5646, and she says that you can rent a 250 gallon greywater container from them for $500 and they will just pick it up at the end of the event. This needs to be arranged 30 days in advance.
She also said that you can flag down the drivers of the sucking trucks and they will suck up greywater for $1/ gallon! There's no excuse now for dumping greywater on the playa if your evap is still full by the end of the burn!
I hope this helps!