There's a magic trick - a disappearing act - that people try not to think too much about. It's a marvel of engineering, but much like the Vanishing Cabinet trick the audience doesn't really want to hear about the engineering aspects. They want the box they're familiar with, and they want the assistant to step inside and disappear... and then they want to stop thinking about it. Of course, the metaphor falls apart a bit here because the thing disappearing is certainly not a lovely assistant and you absolutely don't want it to ever reappear. But I digress.
On my first flight to Mars, I was stopped by Customs in orbit. This didn't bother me. I had followed all the rules and if some of my passengers had illegal fruits or vegetables that wasn't my problem, it was theirs. They had all signed waivers. What I failed to realize is that several passengers were carrying things far worse than strawberries - though in my case strawberries are pretty terrible since I'm deathly allergic... there I go again. Sorry, back to the story. Where was I... oh, right, one passenger was also wanted by the law and felt certain that this was not a routine customs search but a roadblock set up to capture him.
I was oblivious, cheerfully setting up the docking protocol with customs and not once wondering why there had been a rush on the bathroom. I didn't think for a second that three separate passengers were dumping things into the toilet that didn't belong there. A zero-g toilet is a bit daunting at first, but once you're used to it going to the head really isn't that bad. There's an arm that comes down like a tray table to help you stay seated, and a lot of extra buttons, but in essence it's still a toilet. That first time, though? Having never prepared for this? Terrifying. That feeling of air rushing past your exposed undercarriage is totally foreign - on Earth we have gravity to take care of our waste disposal. You get used to the air flow, like you get used to anything, and you don't stop to wonder about the mechanics of it. And I've digressed again.
Three people went in, dumped items, and ran out. A fourth grabbed some nice young woman by the hair and dragged her into the head with a knife to her throat, screaming that they would never take him alive. This turned out to be correct, but I guess I'll get to that in a second. Sorry. Anyway, I learned about this at the same time as the customs agents and we were all just as shocked as each other because they hadn't been looking for anyone, they really were just checking for fruits and vegetables.
They weren't expecting illegal drugs, which had been dumped. They certainly weren't expecting banned chemicals (being smuggled in to keep outdated machinery running even though it had been declared environmentally unfriendly) which had similarly been dumped. They absolutely were expecting some illegal booze, but wouldn't find it because that, too, had headed down the drain. For myself, I wasn't expecting those items to all end up in the toilet at the same time and have some sort of reaction.
What people don't want to think about is where bodily waste goes. It disappears, like magic, and they're happy about that. Those who have some idea will tell you that the liquid is spewed out into space and the solids are compacted, exposed to the vacuum to sterilize them, and then stored. They're forgetting some things, because like I said nobody wants to think about how that particular trick works. One thing they forget is that the process of separating solid and liquid isn't instant, and so if a few people use the head in rapid succession it all gets to mix. The second is that there's air - it's that gentle flow of air that directs the waste in that zero-gravity environment and it needs to go somewhere too.
We don't throw out air in space, so it gets filtered which is fine if it just contains some ammonia and bacteria but if it's a cloud of corrosive gas from a freak chemical reaction it could do something strange like melt through into a fuel line and dump that into the mix as well. I'm not sure why they put that fuel line there, I tried to ask an engineer once but it turned out he had only designed... there I go. Back to it, I apologize.
So, as the customs officials ran over to negotiate or shoot the guy or whatever, the system that heated and separated the waste kicked on. The toilet seat headed off towards Mars and knocked out a satellite, doing millions of dollars of damages. It was spectacular. It also left a hole in the ceiling, out of which rushed some air. Just some, though, because that poor bastard managed to plug the hole nicely with his body. The air pressure wasn't enough to crumple him and suck him out right away, and the girl got out of the bathroom and slammed the door. The guy lived through this part, at least long enough to see the system back up and vomit compressed blocks of human waste at him. Fast. Not a great way to go.
The real problem for me, of course, was that the filter had melted and for the rest of the flight the whole ship smelled like a giant fart. That's why they... oh, I'm sorry, you just wanted to know my lunch order.