Cleaned a filthy window today, gave it plenty of water and scrubbed twice over. Bad news - customer phones an hour later complaining of water inside the house, all down the wall with the plaster swelling up!
I dashed back to check and sure enough the inside is saturated, plaster bubbling up and water all over the inside sill.
Turns out the seal is slightly twisted and the drainage holes aren't draining. I poked a wire down but find out they haven't been drilled through.
Get a drill out and bore the holes right through and the water pours out (loads of it). Customer by now is going berserk and getting very abusive. I told her where to go!

The good news .............. it's my house!
Hope i don't repeat it on a customers property. :
