And now, a little insight from the less glamorous side of trucking...
I have a 5 gallon bucket I use when I'm placarding one of our rental trailers with the adhesive placards. Sometimes I'll have up to 10 placards to put on each side, so the bucket helps to hold the placards and then the backing once I peel them.
Anyway, twice, and only twice since I've been driving (which isn't as long as some of the veterans on here) I've been in some, well, ummm... "intestinal distress" with no facilities available. So I did what I had to do- opened the vents, cranked up the fresh air A/C, lit up a cigarette, and popped a squat on the double-bagged 5-gallon bucket. And then drove with the windows open for a bit.
I also have a case of baby wipes as well- great to get grime off the hands and also for those rest area nights when a shower is not available. They also are great for, well, wiping your butt.
Do your business, tie off the inner bag, tie off the outer bag, and dispose of properly.
It aint glamorous, it aint pretty, but sometimes in the middle of nowhere you gotta do what you gotta do and I lost my affinity for those fresh-air bombs back in my boy-scout days.
Maybe one day if I own my own KW with the 86'" studio sleeper with the accompanying storage space I'll get a proper camper's porta-potty, but fo now the bucket has served me well enough.
-p.