Yes it's a good rule, just never thought I hear of it on Playa Sosua.
I don't expect to see police checking for glass every day, possibly on Sundays, which are very busy, or maybe not until next Samana Santa, but they were today.
If somebody showed up with glass bottles, like the person in these photos, who had a 1/2 gallon of vodka, the police held the bottle until they came back with plastic water bottles and transferred the contents of the glass bottles to them.
To get these photos, i had to wait until there was a clear spot between me and the checkers. With the second photo, there was a momentary opening, but I had to shoot fast so was not properly focused. But it is clear enough to see the transfer of vodka.

