I use refractometer instead for pre-boil gravity and post boil, then a hydrometer for final gravity., so only need a sanitized spoon to pull a little wort and put a few drops on it. But easiest way with a hydrometer, is to take a sample from the spigot if your kettle has one, or get a wine thief. They are literally made for pulling a sample for the sample tube.
There are two basic kinds of wine thieves, one where after you dip it in the wort, you put your thumb over a hole in the top and it keeps the wort in place, then you let go to put in the sample tube. The other, which I prefer, has a little pin on the end of it. You put it in the beer and move it up and down to pull a sample (the more you move it, the fuller it gets), then you touch the pin to the inside of the sample tube, and the beer releases. I believe Fermtech makes this model. Whichever you use, remember to sanitize it before putting it in the beer post-boil.