Many hikers only see the first couple of miles of this trail, since Lily Lake is a popular location for families. But the Clear Fork Trail is many miles long, and offers fantastic adventure past the small lake.
From the trailhead for Lily Lake, hike a relatively flat trail to the namesake lake. Take a short break at the lake, then carry on. The trail climbs moderately for less than a mile to a broken-down shelter at a junction with the Clear Lost trail, which heads right, and eventually ends at a junction with Packwood Lake and Bluff Lake trails, about a mile above Lost Lake.
Your route, however, is straight ahead. Drop down to a small creek crossing, and head into the forest. It's mostly-flat, forested hiking for about 6 miles through here. That means you have lots of time to gape in awe at the huge trees around you: Doug-fir of course, but also yellow spruce and hemlock. The forest floor is spongey with their needles, and makes for soft hiking.
Along the way, you'll have three major creek crossings, none of which have bridges. Most can be forded safely in low water, but as always evaluate the flow and decide if crossing is safe for you on the day you visit.
Your final creek crossing (this one of the namesake Clear Fork) is 6.5 miles in, just before the trail begins to climb to its junction with the PCT at Tieton Pass. Take a break here and regroup; another quarter-mile down the trail, there's about a quarter-mile's worth of major blowdown ahead that will likely require some routefinding. Once past that, it's smooth sailing (though possibly slow-sailing, since you'll be climbing steadily) to the trails end at Tieton Pass.
From the pass, turn left or right for the PCT, or continue straight ahead to get on the North Fork Tieton trail.