Guild Wars 2

So my Engineer puts four rare armor pieces – all medium armor – into the mystic toilet and out come heavy gauntlets, soulbound on acquire.
I can’t wear, can’t sell it to a merch, can’t transfer it to another character, and can’t salvage it.

Is there anything I can do with this other than throw it away?
Or put it back in the toilet?

Put it back in the forge. The forge can generate items you would normally get from a Karma vendor, which are soulbound on acquire. If it’s something you can use, check the skin before you toss it back in. Sometimes they’re interesting.

If you want to be guaranteed the same type of item you put in, you have to match them, e.g. put four medium gloves in. You’re straight up gambling when you toss random items in there. I enjoy it, but it’s not really a good way to make money or upgrade your gear