Our ALSE shop always has spare flight suits.
Also, you should have three flight suits so if you need one changed, you should have two more to get your through until you have your third one again.
4 is our entitlement, and in a situation where you're only doing local flying and LRPFs, what you say above does and would work.
But, LRP goes out the door
very quickly sometimes. The situation I mentioned in my reply to PC above isn't fictional, it was my crew on Labour Day Weekend a few years ago.
On that Det, we were flying nights, sometimes back-to-backs, and the only viable laundry solution was to drop a bag off at a local place, and pick it up a few days later. Working outside in the rain building/loading belly loads, uploading internal loads, and then putting patterns into the water can make a flight suit a "one mission deal". 2 flight suits aren't going to last too long, especially on Dets like CARIBBE.