? I've never worried too much about the washing, as I've assumed that any chlorine/salt etc is going to be harsher than my non bio or soapnuts. My costume gets a rinse in the shower after a swim in a pool, or not if at the beach, then bunged in the machine with the towel and a load of other stuff.
I either rinse them or if I have been slattern like and forgotten to get them out of swimming bag will wash them. I am sure this fades and wears them out(only DD and mine - DS's are fine) but I get cheap ones and DD keeps growing anyway.