A long time ago I bought a Sci-Fi or Fantasy book that was one of those collections of short stories by various writers - this was probably 10 years ago at a used book store, so no idea how old it was. One of the last stories in the collection was called "trash". In it a guy was using a worm hole to put his trash in, and whoever was on the other side of the wormhole was not pleased. I've been trying to find it again, but so far no luck. Does anyone know the author or which book it was in?
This is a provisional answer because I can't remember what anthology I read it in so I can't check the details. However I think this is a story called Litterbug, and some Googling suggests it was written by Tony Morphett and published in The Magazine of Fantasy and Science Fiction July 1969.
I have a somewhat fuzzy memory of reading this as a teenager (forty years ago!). I'm certain I didn't read it in the magazine so I would have read it in an anthology. Possibly in Beyond Tomorrow as that would have been about the right date.
My recollection is that an Earth scientist invents a garbage disposal device based on a portal/wormhole and everyone starts using it. All is well until some very annoyed aliens turn up!
If the story was from the perspective of the person on the trash-receiving end of the wormhole, it might have been Singularity by William Sleator. Some teenage twins discover that their eccentric distant uncle has died, and go to his house to see what he left them. There is a reinforced shed in the backyard.
The narrating character (one of the twins) figures out from his uncle's correspondence and an accident where one of them was locked in the shed for seconds outside/hours inside that the output from a singularity (everything is sucked into a singularity, but the matter has to go somewhere) is in that shed, so his uncle had been collecting alien trash and some unusual dead bodies from it.
Later, the narrator spends extended time in that shed, and one of the major plot points is that something big (or maybe it was "still alive" - I don't remember exactly) is about to come through and he's not sure what will happen when it does.
Singularity was a fairly short story, but I don't know if it has ever been published in an anthology. On the other hand Sleator is prolific enough it wouldn't surprise me if his stories were included in one.