Trex should never be sanded. Sanding will change the appearance and protective qualities of the Trex composite material and will void the warranty with respect to any condition caused by sanding.
Trex high-performance decking (Trex Transcend and Trex Enhance) can be power washed. Use only a fan tip and up to a 3100 psi power washer to remove soil and debris. The fan tip should be no closer than 8 inches (20.4 cm) away from the protective shell during use.