That took me a minute. It is a moronic vulgar expression somebody made up to mean that he is urinating. It is not in common use—I had to figure it out.
By the way, I don't know where they say "abseil", but I had to look it up. It is a word, all right, but we say "rappel".
This was a translation given by Google Translator. I had no idea it was vulgar. However I didn't like it, it just sounded odd to me so I posted it on the forum.