So you ordered yourself a new Ultimaker3, cool !! now you need something to keep your PVA dry as it's deteriorating super fast when left exposed. The Ultimaker advice is to store it after use, don't leave it on the printer. My advice is store it even when printing :) .... these dual prints can take a long time. Basically I just put together a closed box + spool-holder + holder for the moisture absorbent. I feed out the filament at the side of the box, just using a small piece of bowden tube. I made one for PVA and one for Nylon. I place the box on the left of the printer for material entering the right feeder.