I go through about 8-10 mls per day, tobacco flavors, I mix them at about 5% flavoring, and a lot of times will cut that 50/50 with unflavored. I mix at
60pg /40vg, or 65pg/35vg. I have tried the rinsing/ soaking in alcohol thing, and I can get another day or so out of them, but that's about it.
I'm very picky about how my vape tastes, for instance, I like the ProTank 2 because I can easily re-wick the coils with cotton, and do so at every single fill, as soon as the cotton gets the buildup in it, I can taste that and don't like it.
Back to the Nauti coils, I don't just toss them, I pull them apart and save the res/ no-res wires, the cotton is always blackened and the coil is loaded with carbon when I dissect them, so I know my taste buds aren't lying to me.
The 4-5 days time I gave is for situations like when I have traveled, and relied solely on my Kabuki tank, in day to day life, I'm running two Kabukis and a Nautilus, two Cerotanks, a ProTank, two Z-Atties, and a good handful or REOs mods and a couple drippers, grabbing whichever mod happens to suit my fancy that particular day, so I go solely by taste on when I yank the coils, when one tastes funny to me, I'll drain it, and fill it up with un-flavored e-liquid. After about half tank, it will either improve, or the "burnt" taste will remain. I just trust my taste buds on this one.