cleaning recommendations would be easier if we knew just what it is you are trying to clean out of it...soap scum? hard water build up/lime? fabric dyes? dirt?
my deep fiberglass sink i pour about 1/2 a gallon of bleach into, finish filling with hot water, and let it set...til i'm ready to deal with it again...then i simply take a sponge on a handle and scrub around with it, drain, rinse...beautiful until the next time. but it depends on what is wrong with yours what is going to work.