I soak mine in hot water (not boiling it ruins them) then I use a non-perfumed soap and rub them together and all the gunk comes off. The soap has no smell what-so-ever. I bought it at a pharmacy for myself because my skin is a bit sensitive to any soaps or lotions with perfumes in them.
After that I just shower them off in hot water for a few minutes to make sure no soap is still on them. I've done this quite a few times now and all my fish are fine.