If you are planning to go to Flying Fish directly from DHS, you can take the Friendship boat and get off at the first stop (Swan and Dolphin) and walk over the bridge to FF. You can see the restaurant from the dock. If you want a little longer ride the boat will go to the YC/BC and then back across the lagoon to the BW where FF is very close to the dock. There's also a walking path from DHS to the BW.
You can also take the Friendship boat from DHS to Epcot and spend time in the park. Leaving Epcot you can take the boat to the BW (first stop) and Flying Fish. You can also walk from Epcot to Flying Fish.
The boat route is:
DHS --> Swan/Dolphin --> YC/BC --> BW --> Epcot
return is Epcot-->BW --> YC/BC --> Swan/Dolphin --> DHS