The Southwest Chute of Mt. Pinchot starts in the small basin just north of Pinchot Pass. Pinchot Pass is along the PCT, between Taboose Pass Trail to the north and Sawmill Pass Trail to the south. Take either of these trails out of the Owens Valley, and head to Pinchot Pass.
There are a handful of chutes heading up the Southwest side of Mt. Pinchot. The one you want descends directly from Pinchot's shorter Western summit. It begins immediately to the left of a sheer looking pinnacle on the Western summit. The bottom of the chute leads to a higher ridge of land (visible on the topo) that extends towards Pinchot Pass. This should help you find the right chute.
Once in the chute, go up. This is a very loose scree slog with lots of loose blocks. Recommended as a DESCENT ROUTE only.
To find the chute from above: from the summit of Mt. Pinchot, traverse west along the ridgeline, staying to the south side, but not far, as you must attain the very top of the Western Summit. Go to the very highpoint, and then do an easy Class 3 move or two down into this long chute. The entire steep chute is viewable from the western summit. Go straight down, taking care not to knock loose blocks onto your buddy.
A helmet will be critical, as loose rock abounds.