how do you get rid of junk
You don't really need to.
But It can be used to craft a few items after only the Parasite cleanup in New Ark Lab, use a few Junk to craft two items you could use in the BDSM dungeon.
And after that I don't recall a way to really dispose of items in LD+
Just sell it. You won't get money, but it will remove it from your inventory
No you cannot.
It's not possible to sell Junk the game disallows it.