On Thursday, 6 May 2021 at 19:39:22 UTC+1, rick wrote:

Many of the Fatbergs come from Takeaways / restaurants running without
grease traps

It is, therefore, obvious that such establishments (whether takeaways, sit-ins, food factories, or whatever else) should conform to grease trap requirements before they open. And become responsible for failure to do so.

Getting back to an earlier point, if we know the fat is coming from such places, then the positioning of sensors (of whatever sort) should be fairly obvious.