If I legally sell a gun to someone, it's not my responsibility if the buyer then shoots themselves in the foot with it. That's now how responsibility works.

Your comparison is silly because contract killing is illegal. Selling garbage isn't.

Why is it the responsibility of other nations to make sure that the Philippines can handle the amount of trash they're taking? That makes no sense. Sure, countries should handle their own waste issues, but no one is forcing the Philippines to take anyone's trash. They're doing so freely, and then immediately mismanaging it. It's a self-inflicted wound, and no doubt people in government or business are getting plenty of money out of it while the average person wades in garbage.

I'm not absolving them, but plenty of nations get trash and it doesn't end up in the ocean to anywhere near the degree that it does in the Philippines. So they should be taking only what they can actually process. Again, they're under no obligation to take anything at all.

It seems they only said not to after it was already sent and discovered the sending company had lied about the contents. It's still a problem with the local government, though. They take in far too much than they can handle, and it seems that most of the so-called "recyclables" are simply dumped. At any time, though, they can end or drastically reduce trash imports officially. They have the autonomy to do so.

This seems like an issue with their government then.

But why buy someone else's garbage in the first place if there is no real infrastructure in place to handle it properly? If they're overwhelmed, they could say no more at any time.

If they can't handle it, why are they taking it? Even if the problem is the Philippines taking in the world's garbage, the problem remains that they're mishandling what they're taking in. They can say no and make other countries handle their own trash, so I'm guessing the government likes the cash more than they like a healthy environment for its citizens, let alone the ocean.

Is the Philippines forced to take anyone else's trash, though?

Technically, it comes from waterways emptying into the sea nearby. Cut off the trash entering the ocean to begin with and you won't have trash washing up on the beach.