A window cleaner i know used to remove the top from the di tank, but leaving the tube thing in there, he said it was easier that way, but i cant imagine how?!. When i used di, i just took the whole lot out, rinsed the tank with some water (probably not necessary), filled it up (just over 3/4) with dry resin, then put water in (just normal tap water as i was di only at the time) till you can see it on top of the resin (dont fill the water right up as when you put the tube back in it will spill water and resin out all over the place) the water makes it easy to get the tube back in, assuming you havnt put too much resin in. I found it difficult at times to get the thread right, so what i started doing was to push down on the top whilst turning it backwards till you feel it 'drop' on to the thread, then you know it is sitting correctly and you can tighten it up without fear of damaging the thread.