[Arran]

The mix I would start with is maybe about a tablespoon of TSP to a gallon of hot water, just to make sure that it isn't so strong that it takes paint off, if that doesn't work then you can up to two tablespoons. I don't spray it on but you could put it in an old spray bottle to make it easier, let it sit for a few minutes, then rinse it off with more hot water, and let it air dry. Maybe you could do this in a bath tube or a laundry tub?
Regards
Arran