When cleaning soap scum from a porcelain bathtub, I sprayed 409 and then went over it lightly with Scotch-Brite stainless steel scrubbing pads. Not sure how long the scum was there from previous owner, but it came off and didn't harm the finish on bathtub.
By JS from WI
Soap scum build up on a tub can be very difficult to remove. This is a page about removing soap scum build up from a plastic tub.
