Just save it in the fall after it gets hard and durring your winter cleanups. Messing with it in the summer is way too messy. Scrape it off with your hive tool and toss the hard bits into a mason jar and save it. You can make alcohol tincture out of it with your favorite brand of vodka. I put about a cup of propolis in with a pint of 80 proof, seal it up good, shake it once a week for about 3 months and you have a tincture that you can take a dropper full each day. If its too strong because you used everclear your first time you can use that to paint on the interior of your hives and swarm traps to give them that lived in feel/smell. Its real easy stuff.
I will see how much I can collect this year.
In some ways, more than the honey, and wax, I’m amazed at how fast bees can bees can produce propolis.