Do you have to wait for the whole thing to drain before getting a refill, or can you get a refill still if there is a little bit left in this thing?
don't have to wait. But the gas service company will have to dump whatever gas is left in the cylinder to be able to "zero out" the scale and accurately fill the tank... Even the big companies like WESCO and AIRGAS weigh their cylinders. Cylinders all have varying weights. To get an accurate fill volume, they empty the tank, zero the scale, and fill it from that zero point. A 5 lb tank will usually get 4lb 15oz to allow for expansion - especially in the summer. Higher external temperature will increase the pressure in the tank...