Originally Posted by
flyerCO
On international flight TSA regulations come into play. On flights departing the US only passengers in that cabin are supposed to use the lavs. (At least this was the case at one point) Otherwise everytime I've heard an announcement on other flights, they requested passengers do this, but they still allowed it.
You have it backwards. It's on flights TO the US where for TSA/DHS security reasons, passengers must use the lavs in their ticket cabin. I'm not sure why the difference exactly, and why it's less of a threat on a flight outbound from the US versus to the US (the only thing I can think of is different or unknown security vetting of flights to the US versus flights from the US where passengers went through TSA security), but that's the policy.