There are laundry facilities on Riviera deck mid/aft, Main deck and Upper deck both aft, Empress deck forward, Verandah deck mid/aft. I don't know if they are starboard or port. You'll have to just look.
the laundry room is on the 7th deck across from room 7279 in that general area there is a second one but I did not use it we were in cabin 8181 so we only had to go down 1 flight of stairs
I did laundry when we were on the Elation. (Mexican Riviera Cruise) We were going to Disneyland afer the cruise and so I planed on doing a few things so I would not have to pack so much. I would never do it again!!! I had to pack my clothes into a suitcase, carry it up and over a floor to this very small, very HOT room, put my clothes into a machine and then take my suitcase back to my room with me. There was no place to sit and wait for my clothes. It was just to much running back and forth. Way to hot in the room too. Next time I will just pay the laundry service fee or pack extra.
My experience on the Elation was the opposite. I found it totally easy. I was traveling with four kids so it was definitely necessary to do some laundry. The machines were always available. Just bring your own powder. the machines are very expensive and you don't want to add any more overpriced things to the equation! I think it was 2.00 to wash and 2.00 to dry.