I use a syringe with a flexible tube and 91% isopropyl alcohol to clean my Boges and Echo-e's, then I let them dry for a week. Every Saturday morning I'll have a handful of cartos to clean. The task takes maybe 10-15 minutes total. I have yet to pitch a carto, and some have been cleaned as many as eight times.
The key may be to not let them get funky, but rather to clean them before they get to that state. I vape mostly clear e-liquids, and I chuck the cartos in the to-be-washed bucket after no more than a week, even if they are fine in terms of vapor production, draw ease and taste.