The main issue is priming the carto successfully.
I used to say "50-70 drops", but now I tell people to drip ten-twenty drops directly onto the polyfill while holding the carto at an angle, avoiding the centor hole, rotating the carto after each drop (like a gatling gun). Then give it a nice, hefty thermometer shake. Put some inertia behind it. Then continue to drip ten-twenty more drops. Then give it another thermometer shake. Then drip more drops in. When juice comes out of the little hole at the bottom of the carto on (what should be) your last thermometer shake, it's sufficiently primed.
It's better to over-saturate a carto than to under-saturate during priming. If you over-saturate your carto, you can simply place the connection end in a balled up paper towel and blow the excess juice out of the carto. You should be able to hold the carto up to the light and see a clear, unobstructed pathway entirely through it (hold it away from your eye, but look through the top end like a telecope). If you under-saturate it, you run the risk of burning out the carto the first time you press the fire button.
I just need to find a decent camera set-up, and I swear I'm going to upload a how-to video for priming and filling carto tanks.
