It's like any mixing service, put in more than you need and split it out, or submit it in smaller increments and take it out as one lump sum, or some combination of the two. You can do 3 in and 3 out, but make them different amounts coming out and don't send them to the same address. I don't trust mixing services like blockchain.info, where they charge a flat fee of 0.5%. So you send them 1 BTC and a few minutes later there are (always) exactly two transactions to the same address that total 99.5% of the other one. Anyone looking at the block chain can figure that out, especially since the transactions are so close to each other.