For me, once the unfiltered oil is all sucked up and there's about 30mil in the tubing, I just lift the tube up so the vaccuum sucks thee last out the tube, once that's gone, air does get into the filter, once it stops dripping then I dis-connect.
So IB do you suggest to leave the filter full of oil when its disconnected? I'm fine with that is if works, only thing I'm thinking is, when its re-connected to a new batch, the tubing will be full of air so it will suck in the air out the tube before the new oil reaches it if you get me?
Maybe the filter gets some sort of air lock? I still don't understand how its blocking. The new batch of oil sucks up so far, to the hight of the filter then just stops fead in the tube, the vacuum must be getting jammed at the filter from pump to filter and not reaching the oil enough to draw it in..