Once you have made your way to the other side of the Waiau River from nearly Harbour (either by way of water taxi, kayak or private boat), follow the way up the river towards Lake Manapouri. The first 15 minutes of the track are along the lake.
When you reach the junction with the Circle Track, continue straight until you reach the next junction with Hope Arm. There is a track from Back Valley Hut to Hope Arm Hut, so it is common to do this as a loop track.
If you are only doing the Back Valley route, follow the track leading left. The track leads through beech and podocarp forest and a stand of ribbonwood. It then open up onto some small clearings, where the Back Valley Hut is situated.
If you have some time to spare, there is also a side track from here. You can reach Lake Rakatu in about an hour, the whole detour taking less than 2 hours. Many people come here to fish for the day before heading back into town or spending the night at Back Valley Hut.
Return to Pearl Harbour the same way or complete the loop with Hope Arm Hut.