A teenage worker taking out the garbage at a Long Island Dunkin’ Donuts Sunday night fell into a cesspool and died, police said yesterday.

Amiri Zeqiri, 17, slipped into the open pit behind the shop in Smithtown, where a manhole cover usually is over the cesspool, police said.

The teen’s younger cousin found Zeqiri in about 8 feet of water and ran to a nearby store for help, but when he returned, the teen was no longer visible, police said.