Question : how do I bypass fax detection for a specific DID and go straight to fax tones?

I'm running trixbox 2.6/asterisk 1.4.  Sangoma T1 card on a T1 PRI.
Some people call our fax line and the fax detection thinks it is a person instead of a fax machine.
How can I get the system to simply assume that any inbound call to that number is a fax, and have it start the fax receiving routine?

Answer : how do I bypass fax detection for a specific DID and go straight to fax tones?

That has to be done in a dialplan. Given you are using trixbox I suggest you ask in the trixbox forums.