Put vinegar, sugar, salt, clove, and allspice in a large nonreactive saucepan. Place over high heat and bring to boil. Put the onions in a large, nonreactive bowl and pour the boiling pickling liquid over them. Toss well. Allow to sit, tossing occasionally, until cool. Onions will wilt and turn pink. Let sit for 3-4 hours before using or refrigerate for up to 5 days.