Muckenhirn cleared waivers Friday and was sent outright to Triple-A Tacoma.
The Mariners DFA'd Muckenhirn on Wednesday, but he will remain in the organization after going unclaimed. The 28-year-old reliever hasn't pitched for Seattle in the majors since being acquired from the Mets in July, and he's put up a 9.35 ERA and 1.95 WHIP through 8.2 frames with Tacoma.