In message , John
Rumm writes
AlexW wrote:
The other nice one was the previous builder had fitted an extrator fan
in the shower. It was mounted on the dry lining, and ducted through the
inner course of brickwork. But there was no matching hole in the outer
course - so it was simply filling the wall cavity with wet air!

As I may have said here before I think one of my favourites was done by
my present homes previous owner. The over flow from the bathroom toilet
exited the cistern into the outside wall but did not come out on the
other side so if the ball cock had ever failed it would have overflowed
into the cavity. Not to mention the 2.5mm power feed to the electric
shower.
--
Bill