Hey Icey, Spoke with you a while back. The wife and I just bought a few 3.5ml tanks and so far we are pleased with them. For us, the full tank will last all day. I do pop the drip tip off and drip a drop or two every now and then to "help it out"
If your asking about the carto time till spent, We generally run ours about a week. Sometimes more, sometimes less. Depends.
Im excited to see the latest craze of tanks and things but they need to improve on the material the tanks are made of because we have had some crack in 1 days time. Buy a couple to be safe. I'm thinking bout buying some ss tanks from
BDV Lil' Mama 3ml Tanks : Big Daddy Vapor
Take care, hope this helps