Ask these guys, I think they have the bubble figured out.
Just let the sample sit for awhile (eventually the bubbles will go away). Another option is to roll up a piece of paper towel is it will fit inside of tube. Take the hydrometer and it push it down, which will force the liquid up, then remove the hydrometer. This will lower the level of the liquid, but the bubbles will "cling" to the sides. Wipe them off with a paper towel and repeat.
It sounds a lot more complicated in words, but it literally takes 2-3 seconds to get rid of most of them.