I have been through this 3 times w/ angel in the past year. (Thank goodness for care credit!!!)
Thank goodness never a blockage, but lots of struvite crystals in the bladder. They were visible during an ultrasound. I agree w/ everyone else. Angel is now on Purina UR, (after trying everything else) & will probably have to stay on it for yrs. if not forever. (I also still mix filtered water in w/ his food).
I have been able to catch a sample by just quickly, but swiftly swooping under him from behind just as he is squatting. HOWEVER, it is hard to get a good urinalysis form this, & they usually want a "fresh" sample, which means slightly sedating her for a catheter to be used.
When I have done it, I made sure the container (small, shallow jar) was very clean, then put some alcohol in it to shake it around, (to get the inside of the lid too), then let air dry for sanitary reasons. This way, I know the jar is sterilized. The most important thing is, you HAVE to get it there with in 20 Min's. or so. If it sets to long, it will develop crystals on it's own, & that's why it's hard to get a "real" sample reading from it.
I have threads I started each time angel had one, if you want to check them out for info as well. I got a lot of great advice from others on this site.
I would strongly recomend LDG's thread as well, as she is the main one who has helped me so much, so many times!
I wish you luck with all of this, I know it's not fun to go through! Keep us posted.