What can I do about moldy plumbing fixtures?

Certain types of black mold can kill you. Make a solution of bleach and water, half and half, and spray that down, including the shower walls, the entire toilet, and your sink, then clean it. You may have a condensation problem causing the proper environment for mold there, which may mean you have black mold behind the fixtures, maybe inside the wall and under your stool. use that bleach-water every couple of days, until you've gone through a gallon of mix. Hopefully by then you will have killed all the spores. Make sure you have good ventilation, and you probably should wear a dust mask.  more