I've been doing this for years, with bucks and does.I take two 35mm film cannisters to the field (they're waterproof). I don't use a syringe or anything. After the deer is gutted, I find the bladder, follow the tube down a bit and cut it. I then just squeeze the bladder while aiming the tube in the film cannisters.

I refrigerate it andcut it with water (50/50) to make it last longer, and take it to the field in a squirt bottle. I only cut what I transfer into the squirt bottle, and then onlywhen I'm ready to take it out.Any excess at the end of the season, I freeze.

Some deer have little or no urine. A few years ago I killeda button buck, his bladderwas so full there was no way it was gonna fit into two film cannisters. I cut the tube leaving a generous length, then tied it off with string and took the bladder and all. It was a little bigger than a baseball, getting to softball size.