Because I live in a windy desert environment, theres always dust blowing around outside to some degree. I've refined my technique down to a t, for my area. YMMV.
The reason why I leave it to drip? Because I'm not gonna let it sit there waiting for the last 5% to drip out (on a okief xl or similar, after doing 3-3.5 cans), it will drip out a couple of grams after the lions share of the butane runs through. It takes way too long, I'd rather just set it off to the side while I'm getting the main part evap'd. It really does drip out quite a bit: ask my buddy, he found out the hard way after he semi-ruined the finish on his table, thought it was done running out (his lady just about killed him).
Not really concerned about the tube being hard to clean, it's not hard to dump it out and use a bit of alcohol to clean it out. (remember, I use stainless extractors)
I use a basket ball inflation pump to blow out the last bit of liquid.