If you're renting through a member, then you should have a copy of your confirmation. On the confirmation it will tell you which day is your full cleaning and which day is your trash and towel day. You should have one of each during an 8 night stay. If you are only a seven night stay (8 days), you will only have one trash and towel day which will be after your 3rd night. Your tip, if offered, is based on the size of your unit. If you are a studio with one bathroom it would not the be same if you're a 2-bedroom with 2 bathrooms and kitchen.
If you stay at a DVC resort that you rent through Disney and paying cash per night, you then get daily mousekeeping like any other resort and you should tip accordingly if you choose.
BTW, unlike the poster above, we have always had extra trash bags available to us in our DVC unit. Most of the time they are under the trash bag, so you see them after you pull the trash bag out. There will be a room where you can drop your trash off at.