One for comments, one for pages, and one for posts. I’m not sure if that is the correct way to go about it as I’d like one trash can to rule them all with a drop down box to select different items.

Yeah one global Trash Bin would be best imo. I've been hanging for a feature like this for a long time, I just hope Akismet spam comments don't end up in the bin when deleted, the Trash Bin will get full very quickly.