I just got a backpacking permit for The Needles this weekend, and this is what the Backcountry Packet included with permit has to say about the subject of dealing with waste. Good news for backpackers!
Whenever possible, human waste should be removed from the backcountry. A washable/reusable toilet system or human waste disposal bag is required when camping at the Maze District vehicle campsites; at the New Bates Wilson site in the Needles District; and within ½ mile of the Green and Colorado rivers. Toilet paper must be packed out of the backcountry. Backpackers are encouraged to use bag systems in order to prevent the build up of human waste at designated sites. Bags must be of the type that use dry chemicals/enzymes to render solid human waste into nonhazardous products acceptable for disposal in permitted landfills. Waste disposal bags cannot be deposited in vault toilets.
The dry soils of the desert do not promote decomposition like forest or mountain soils. Whenever possible, human waste should be removed from the backcountry. To accomplish this, backcountry travelers should use vault toilets whenever possible. In certain areas of the park, visitors are required to bring their own toilet systems. Backpackers are encouraged to use human waste disposal bags, especially near designated sites. Bags must be of the type that use dry chemicals/enzymes to render solid human waste into nonhazardous products acceptable for disposal in permitted landfills. Waste disposal bags cannot be deposited in vault toilets. Solid waste may also be buried in a hole at least four inches deep and 300 feet away from water sources or campsites. If you use toilet paper, always pack it out. Never burn or bury it in a desert environment. Urine is not a health hazard and need not be buried. When camping along the rivers, urinate into the main current to prevent the buildup of odors along the beaches.