Wallet address for the Tumbler

[osagga]

Given how the Q version of the promise protocol specifies that the Cashout Bob creates should have an output of "Q-J" Bitcoins back to the Tumbler.
Which wallet address should Bob use as the destination for the "Q-J" Bitocoins?

I'm keeping in mind that it's not recommend to use the same address twice. Such that Bob can't use the address from the public key of the Tumbler on the escrow transaction.