Don't know how it works for large drug dealers but I would assume they use the same channels as money launderers: overseas accounts.

You get in contact with a connections guy and they give you a list of accounts to pay in yuan (usually business owners that makes profit overseas), they pay you in USD from their legitimate businesses for some made up invoice. Each transaction is under the limit for being scrutinized. Once money is out of the country, you can pay people off however you want.

Prostitutes would probably just take cash if close to limits.