How can you remove cat feces stain on fiberglass bath tub?

Remove cat feces by turning the hot water on and let it run until it is hot. Then, plug the tub and fill it with hot water to the level of the stain. Put 1/2 cup of dishwasher detergent (not dishwashing liquid) in the hot water and mix it around. Let it soak overnight. It may need a light scrubbing when you drain the tub.

A piece of 600 grit wet/dry aluminum oxide sand paper can also be used to wet sand the area.

When the tub is clean, coat it with Rain-X windshield glass protectant. It may take a few applications since fiberglass tubs are porous. This will help the tub stay clean.