As you enter Belfair coming from Bremerton, turn right at the stoplight (just past Safeway). (Pull into Safeway to purchase liquor, etc. Pull back onto the street).
At the stop sign a block later, go straight onto the North Shore Road.
Approx 1 mile past Belfair State Park turn right on the Belfair-Tahuya Road. Stay on Belfair-Tahuya Road and cross the Elfendahl Pass Road (the road that the main trailhead is on).
About 1 to 2 miles past the Elfendahl Pass Road, turn right on the South Spillman Road. This is a gravel road. A short ways down the road, there is a gate which may or may not be locked, go through this gate, staying on the South Spillman Road.
A couple miles from the pavement you'll see a sign pointing you to the Tahuya River Camp on your left.
Just after you get onto the campground access road there is a locked gate. Both of the gates will have the same combination as shown below. If you are coming after dark bring a flashlight, as the combo lock is up inside a pipe so you can't use your headlights to read the numbers.
There should be arrows marked with SMC to point the way.