I'm not sure if this topic has ever been discussed. I'm wondering if somewhere, in all the vast variety of the multiverse, there exists something akin to a gigantic landfill of trash and refuse. This line of thought was spurred recently while watching Star Wars. The trash compactor scene always gets me wondering about what that monster is that we see only a small portion of. I always think of some kind of otyugh offshoot, and that invariably gets me thinking if the D&D setting, with it's ability to magically solve mundane problems, has a location that would fit.
I know we've discussed, at some length, the 2nd layer of Acheron as being a bit of a waste dump - but I don't think that quite fits the character of what I'm looking for. That's more of a scrap heap of rusting war machines and the detritus of war, as opposed to simply garbage.
I'm thinking more of a trash heap that spans the size of prime continents (or even worlds). I suppose some societies might simply deposit a great deal of waste through portals to the Elemental Plane of Fire, which is a nice and quick solution, but offers little in the way of recovery. I'd like to think there's a "Trash World" - maybe a burned out prime planet, now run by a massive clan of nezumi or wererats (I know... cliche) who run the dump and are able to locate things - for a sizeable fee of course.
Alternately, this could be placed on the paraelemental plane of Ooze - which might make an ideal location as the indigenous life forms would be perfect for breaking down the trash - making this sort of like the "recycling bin of the multiverse".
Ooze is in fact the garbage dump of Sigil, and yes, I think any organic matter in the trash will be broken down quickly by a riot of fungi, algae, molds, bacteria, and many, many other lifeforms that find the rich soup ideal.
For a trash Prime, might I suggest the opposite of Ooze: an icy, airless Prime world that underwent some cataclysm in the past that blew off its atmosphere and extinguished its sun. Now unsuited for humanoid settlement, the conditions are extremely preservative. Organic items freeze instantly, metal items have no air to rust in, etc. Great place to dump something you probably don't need, but might just possibly want in the future. It could be run by a few wizards with a lot of constructs, or one of the construct races, or just a bunch of guys with necklaces of adaptation.
A second alternative could be a simple blip in the fabric of the Prime; a mostly empty crystal sphere, with a small sun and an air-filled solar space, and a tendency to interfere with portals across the Multiverse so that occasionally, stuff gets randomly dumped here. Over the eons, the junk has collected itself under the force of gravity and is now a moon-sized heap of garbage. Most of the incoming stuff is junk; occasionally it is people, who are either stuck, or wait around for another random portal to get them off. Some of them have stayed, and make a living picking through the random fall of goods hoping to find something valuable. They often eat what falls (sometimes while it's moving), or use organic mass to compost a small farm area. Sources of water, and spellcasters who can create it, are valuable assets.