There are many stories about the Shackleton elsan, including the females who flew as passengers and who had to divest most clothing to use the said item (and how many forgot to check that the tail lookout was empty first). However perhaps the most infamous was an American airman who we took flying during a deployment to Keflavic.
"Where's the Pee tube?" he asked.
"Use the Elsan", was the shouted reply.
A few minutes later, an embarrassed looking American approached the mission crew.
"I think I made a mistake sir".
He had wandered into the galley and used the oxygen pipe next to the elsan as a pee tube. The look on the faces of the flight deck crew as they turned round to look in disbelief as they were told in glee "...one of the Yanks has just p*ssed into the oxygen system".
The discussion then turned to how far into the system this fluid would migrate and whether it would get past the economiser, with the eng's advice of "don't fly above 8,000ft skipper". Fortunately an economiser change sorted everything out!