The Poison Weapon effect doesn't work. Even if you have poison in your inventory, it doesn't work. If you use the poison in your inventory, then go to use the Quietus 2 weapon, it still doesn't work.
I'm not too keen on scripting or building, but if you wanted to keep this effect (which i think the poisoning of a weapon is pretty nifty) you could have it so that 1 time per rest it spawns 2 vials of poison in the inventory (these would be non-transferable/droppable/sellable) + just an added Idea, as your level of Quietus increases, the poison strength could increase as well.