The only dumpster in Grim’s Quarry is on the community lot. You can dive in the dumpsters in other neighborhoods but you have to hangout for about 2 sim hours before the dumpsters spawn trash, the same goes for the neighborhood you live in. For example in Grim’s Quarry when you arrive at the community lot you will have to hang out there for 2 in game hours before trash spawns in the dumpster. Also, a little tip, you can rummage through the trash cans on most lots now too. You can rummage through the stone trash can at the community lot in GQ immediately upon arriving, there is a cool off period after though. Also when the dumpsters have the strings of toilet paper hanging out from underneath the lid once trash spawns, that’s when they’re really full and you’re chances of getting big ticket items is the highest.