You buy a bottle of DEF from VW. You use up the DEF from that bottle and then either figure out a way to refill it or you cut off the bottom of it and use it as a funnel.
You can read the DEF tank level with VCDS (at least on the cars, not sure about the SUVs).
You only have to service the DEF tank every 10,000 miles. Spillage can be overcome with plastic bags and duct tape which you install/remove each time you service the DEF tank.
DEF=ADBLUE
Bill