If you are on a reservation through Member Services (cash or points), and you are staying seven nights or less, you get trash and towel service on day 4. If you are staying eight nights or more, you get a full cleaning on day 4 and trash and towel service on day 8 and then the cycle repeats. If you want additional service, you can pay for it.
If you are staying on a cash reservation directly through Disney Reservation Center, you get a full cleaning every day.