For aircrew on long missions in cramped cockpits the need to answer the call of nature is awkward. A fighter pilot cockpit obviously doesn’t have the room for bathroom facilities, so relief bags are issued to aircrews. These are clear plastic bags into which an airman can urinate, with a pad inside to absorb urine and prevent spills, smells or infections:
The neck of the bag has a piece of flat wire, when the two ends are compressed with one hand, the neck of the bag is opened to allow the bag to be used, when it it released it shuts closed again:
A yellow absorbent pad is inside the bag, with the bags use, NSN number and date printed in black on it:
Their use is explained by this USAAF fighter pilot:
Now, typically in training, our flights are less than an hour and a half. As long as you don’t drink too much coffee before a flight, it’s generally not a problem. However, in combat, I’ve flown missions as long as 8 hours; crossing the Atlantic, I was airborne for over 10 hours. For these missions, I used what we as pilots affectionately call, piddle-packs.
Piddle-packs are the ultimate long road trip solution. They are specially shaped bags with absorbent beads in them. If we have to relieve ourselves, we’ll unzip the flight suit—which is designed to unzip from the top as well as the bottom—unroll the piddle pack, and then pee into it. Once done, we’ll seal the top, while the absorbent beads turn it into a gel that won’t leak during hard maneuvering.
Tales from the Supply Depot 
The 101’s I worked on had ‘relief tubes’ for the aircrew which led to the outside with the lower air pressure at altitude creating a vacuum to evacuate the nasty stuff outside.
One ‘fault sheet’ writeup purportedly went:
Fault: “Navigator’s relief tube too short”
Fix “Navigator told to think about girlfriend”
So did Broncos which worked great until someone chewed tobacco and used it as a spit cup. The next pilot being quite unhappy at having to pinch off in progress of course wrote it up and the crew chief had to tie a ziplock over the funnel with a cotton screw bag then blow it out with compressed air. Being comm/nav I found it hilarious.
I’ve personally seen the “relief tube too short” writeup, probably due to someone snipping the hose when replacing one. That was signed off “replaced flight suit insert”. (IFF does not work in OFF Mode is also real. )
My first flight chief on Broncos was a prior Voodoo Medicine Man and I have no reason to doubt his story. Seems a particularly annoying pilot in SEA was treated to a reversed slash cut overboard draft tube but I’ve never personally examined those to see if they were long enough to work well in reverse. Those with system-specific knowledge may opine.
Piddle packs have their own pros and cons. When I was at Shaw (33 AMU, F-16s) my Life Support bro TSgt responded to an A-10 whose canopy was closed during Alarm Black for several hours in summer. The pack burst on the seat where the pilot left it running for cover during Alarm Red. TSgt and his Airman went out to swap seat cushions. Airman tried to object when the odor hit him. TSgt pointed to his stripes and that was that.