The pantyhose

He held up a pantyhose. He stretched it out so you could see it had a couple holes in it, and makeup was applied around the holes to give it a look like a human face — mascara around the eyeholes, lipstick around the mouth, blush on the cheeks. “This is the mask. Those of you who’ve worked here before know how it works. You can explain it to the newboots.”
It wasn’t until that night, after lights-out, that Lem explained how the mask worked. If you put the pantyhose on, people could pay to ramrod you up the poop-chute or in the mouth. Standard payment was a full flask of liquor. You “couldn’t tell” who was wearing the mask — really, you could, even if you couldn’t see their face, cuz there was height and weight and tattoos and hair — they all showered together, there wasn’t any hiding who it was.
But it was a rule, Lem said, that every fool on the rig gotta pretend they ain’t recognize whoever wear the mask. You was sposedta call him “Sheila” and pretend you was making sweet love to Sheila’s pussy.
It was not until a few days later that Lem revealed the mask didn’t gotta be a choice. If somebody could force it on you, you had to do it just the same. The rule was that you could plow whoever wore the mask, if you paid the price of a flask — that was it, don’t matter if the masker was begging you to stop or even if the masker managed to take it off before you were done. If the Sheila did get it off, then that “you gotta pretend you don’t know who it was” rule got cancelled — you could call that man a bitch for the resta his life.
So mostly, nobody fought it. If you could force the mask on someone and then get your dick in their butthole, they were better off keeping the mask on.

From Avery’s Adventures in Interracial Manhood