Enema. Called this due to the aftermath rather resembling the above drink.
"Poor old Ethel. She was so bunged up the nurse had to suffer two bum shandy's 'till she was clear.
Emptying a bottle of beer down a girls (or guys if you are that way inclined) ass, proceeding to have vigarous bumsex in said ass, and pulling out rather quickly, for the contents of beer to spray out all over the place.
I gave her the best bum shandy ever last night.