There are no busses from the parks to DD, and no busses from DD to the parks.
The reason for this is to cut down on the locals parking at DD for free, then hopping a bus to the parks for the day. This caused a problem with the spots filling up.
From MK you can go to one of the monorail resorts, then get a bus to DD. From MGM or Epcot, you can go to one of the Epcot resorts to get a bus. And from AK you have to go to AKL by bus first, then get a bus to DD.