If you want to start fresh with a blank mannequin, try this...

In my Riften home, I remove 4 pieces of gear on my dummy, open again to see it's empty then add an amulet, leave the house and come back in to see only the amulet. remove the amulet and recheck to see the dummy has nothing then leave the house again, when I came back in the dummy is empty and nothing respawned.