@smurfy77 Thanks, I actually already added one, but I guess I have to just add more. I guess I just imagined that if dumpster diving is such an essential part of this EP, there should be more of them in the first place.
@Starfree Actually it appears townies can dive empty dumpsters, too. There have been several times, when I've clicked the dumpster and it says it's empty, but then right after that there's a townie doing dumpster diving. And even after the townie's finished, it's empty again.
@Simmerville I suppose that's possible, but for me the dumpster on that one lot has been full every time my sims went there (even, when it became empty right after the first dive) and they've been able to do the dumpster diving immediately. However, on the other two, they have stayed empty, even after they've spent some time on the lot. But I guess I could try to repair my game, if it helps.
@akaniki0 Thanks for the tip! I think I'll have to try the same with the dishes :)