The Orange bus travels from the outpost, up the center of the campgrounds to the settlement, then goes to Wilderness Lodge.
The Yellow and Purple bus run in a circle, turning into the other color at each end of the campgrounds... so if you ride yellow to the settlement, it will become purple to the outpost.
There's a walking/bike path along the river to WL. (Apparently there's a turn off some place that takes you back to a Cast Member break area for recreation and water craft.
Or you can get on a boat.
If you're at the Lodge, you can get on the Epcot bus and that will take you directly to the Outpost if that's where you need to go. I've done this a few times because it's shown up before the Orange bus.