Try Aqua! Yes, it's not cheap, but it's quite anonymous. Every time you receive USDT on Tron, they are automatically converted into USDT on Liquid - a blockchain where nothing is tracked. Nobody knows what you do with those USDT afterwards. And when you need to send them back to Tron, the conversion happens automatically before sending. The link between the received USDT and the sent USDT gets broken.

The fee for this is 1.9% of each conversion amount (USDT TRC20 <-> USDT Liquid). And within the Liquid blockchain itself, sending tokens is very cheap: about 0.08 USDT per transaction.