When I worked my professional internship, I kept mine and washed them. We were a team of 20 interns and only got 5 shirts, shorts, and 1 vest. Since we had a small team, there weren't a ton of costumes and we lived in a townhouse with a washer/dryer included so I was able to wash them without paying any extra in laundry.
My College Program on the other hand, I worked at BBB and had a huge skirt, shirt, and vest and I turned those in every day. The fact that I would have to do laundry every few days instead of maybe once a week or once every 2 weeks and lug it down to the laundry building and pay...I chose extra $$ over spending it on laundry that WDW will do for you for free but we always had tons of sizes to choose from so it was never an issues. They were also dirty from all the hair products, gel, hair spray, etc. not to mention the possibility of bringing home lice didn't appeal to me either! I never had an issue changing before leaving at night since we had to use lockers anyways!