What Figgy said - raise the shower up, or look at rigging up a pump system to get the waste water from the shower into a graywater container. I looked into things like water and graywater service for the camp I was with years ago, and it was cost-prohibitive for us. We were a pretty small setup and relatively broke when it came to additional camp expenses. To inquire about pricing and get something set up, you'd want to give what are now the United Site Services offices in Reno a call. If I remember correctly, you basically set up an account with them by phone (they may need to mail or fax contracts) in advance, and then book the service. They don't do any of it online. Other than United Site Services, I'm not aware of any companies doing that type of work. Anyone doing it would need to have obtained a BLM SRP (special recreation permit) and pay fees to them, as well as be set up with Burning Man's Outside Services - you may want to write to email@example.com
to get more info about approved providers (the deadline hasn't closed for providers to apply for this year, but they'd have info on who did it in years past).