I GOOGLE Searched for mobile RV waste tank pumpouts and found one in Blythe, CA. The following is the firm's reply to my inquiry.
"Hello David,
"Yes we will be servicing all the BLM areas. Since it is a group, we will need to know the dates they will be there, the location and how many RV's want service. It get so busy that we schedule a certain day to do groups. The price for the service is $45.00 per RV. We do the gray and black tanks. Unfortunately we do not deliver water. If you find someone who dose PLEASE be careful. Some say they are a professional water service and are not. Check their equipment and credentials like a permit before you buy. Please have the person in charge of the Beaver Rally call me and I will do my best to take of them. Thank you for the opportunity to do business with the Beaver Rally.
"Best Regards,
"Celeste Barnett
All Pro Pumping
1354 E. Hobsonway
Blythe, Ca 92225
(760)922-6525"
So, Bill, there ya' go. When I parked on BLM at Road Runner for a couple of weeks and to avoid driving into Quartzsite, I purchased a 45-gallon bladder that fit into the backseat of my pickup and purchased a small 120v water pump.