What's the best way to clean the darkened, damaged grout in the corner of my
shower without damaging the tub at the bottom? Any ideas on what to use
(and how to use it?) Swore we wouldn't let this happen when we redid the
bathroom, but here we are. And I haven't got a clue. I want to redo the
corners with new grout and sealant, but she fears I'll screw it up. And I
keep thinking that if I screw it up, I back up and do it again. Right now
nothing is happening, and it's getting worse. Am tempted to take an old
toothbruth and some general purpose cleaner (called Method, in a pump spray
bottle) and see what that leaves me with. Have some toilet cleaner that is
20 percent hydrogen chloride which I know will probably damage the tub
(enamal over steel, or cast iron, looks like), but is there nothing in
between these two extremes?

Thanks for any replies. Haven't been here in a while, and would appreciate
a measure or two of the home repair wisdom and experience that is know is
out there.

Dave