I noticed that to camp near the water in the Glen Canyon area you must possess a toilet that meets the NPS criteria. That excludes toilets that contain waste in plastic bags, except for commercial systems. Does that rule out all the DIY options? In other areas is it legal to use biodegradable bags and kitty litter?
When I climbed Mt Whitney the ranger gave me a WAG bag with the permit. I don't know if the same is true elsewhere.
I don't know if this is relevant but...
I've kayaked/rafted through the Grand Canyon which is highly regulated by the NPS. The standard toilet down there is an ammo can with a plastic liner and kitty litter. The full ones stay on the rafts until the trip is over which can take several weeks. The rafting community still calls that style of toilet a "groover", even after somebody came up with the idea of putting a plastic toilet seat on the ammo can!
The "poo pipe" is required by the NPS for big-wall climbing in popular areas like Yosemite where for some reason its unacceptable to target those below you. Its a standard 4" PVC plumbing waste pipe 1-2 feet long with a cap on both ends. I'm not a big wall climber so I don't have experience with those but on occasion I do wonder about the logistics.
Cheers,
Graham