There is one, maybe 2 laundrettes onboard. They cost about $1 to wash and $1 to dry. You can buy soap at the front dest for about $2.
The only problem you are going to encounter is that you have 2500 guests and not alot of machines. I went one time to the laundry facility and there was a line of about 10 waiting. Waiting!!!! So, I got up early the next morning and when they opened at about 8am, I was ready. By the time I had my 2 machines loaded, there was a line already.
Us the valet service and have them iron your shirts, pants, dresses etc. It's only about $2 per item and saves you alot of time.
Hope this helps.