Once there find the Old Hana School. There is a red-dirt trail along the edge which goes to the left around a point. Keep on the trail it will bring you right to the beach. Blair can give you directions to Red Sand and the Haleakala Park Pools. If visiting Hana for more than one day, do not miss the Seven Sacred Pools in Haleakala National Park.
Nude use is possible in the upper pools on weekdays.
I have only been there on a weekend, when it was too crowded to enjoy without a suit. So I can't yet suggest which pools and paths to take. Find Honokohau Harbor Road. Look for the Boat harbor sign. Hang a left and take the first right.