The product I am using recommends 400 then 600 grit water sandpaper. It works well to clean the deep scum off but on the hard porcelain it seems to just slide around on it. Don’t know if that is enough for the paint to adhere.
I am trying to avoid any paint peel. It is an apartment, I would hate to have to come back while the tenants are in to redo a process that takes three days to dry.
So I’ve gotta get it right the first time That’s the main thing I can’t afford to let it pass… You get it right the next time that’s not the same thing Gonna have to make the first time last.  woo oo oo oo   oops. sorry billy, hope I did justice
Maybe if 400 doesn’t cut it, you can start lower and increase. How about a sanding power tool?
Ok.
Yes I thought about that. Maybe I need to try that route also.
Think I’ll go out and buy one.