I fill them about 20 times or so and then discard them. Tried cleaning them, and it doesn't work very well, unless you clean them only to quickly flush out old juice using a children's medicine syringe, so you can flush air through it to remove as much water as possible (after you flush out the old juice), and then let the filler inside dry completely for a few days. Soaking them in water or boiling water degrades the future performance. Tried it a few times, and quit doing that. Also, boiling water will shrink the filler.
If you have gurgling, it means there's too much liquid in the filler, preventing a good air flow, so blow through the mouth end to remove the excess juice. Crackling is good and normal. Hissing and sizzling is annoying and not normal. I had that problem with a recent batch of Boge 510 cartos, so I switched to KR808D-1 premium cartos to eliminate that problem, and because the KR8s have better flavor.