Well..for what it's worth here are a couple of tips for the carto tanks that I use...and my cartos last AGES. Probably run around 75ml. of juice through one on average, and it's still cranking fine.
First, I like to punch an additional hole above whatever existing hole (if pre-punched) is there. If I'm punching "from scratch" I put one hole approx. where the prepunched ones go, then another about 2mm to 3mm directly above it. Higher up on the carto. I am very careful when punching to not make big holes. I've learned how many turns to make on my little carto puncher and to hold it up to my ear and listen for when the screw punches through. Then I'll turn just a fuzz more...maybe a quarter turn and that's it. If in doubt, I don't risk it...I'll make sure the hole is all the way through the metal by tapping a sheet metal screw tip lightly into the dent I made with the punch. Then I'll check to be sure the hole is clear with a needle.
Prime the carto before filling the tank. I like to use a luer lock needle bottle (one with a sharp needle, not blunt). When I'm pretty sure it's nice & damp in there, I turn the cartomizer over and drop a few drops one at a time into the hole at the battery end. Wipe off and then fill the tank. I like to use either the Slap Yo Mama tool, a drip tip made for refilling like this
http://www.smokerevolt.com/510-Long-Refilling-Drip-Tips_p_412.html Another filler tool I really like is this type
StainlessDCT Refilling Tool
That's about it for my "tips". I love carto tanks now I got the system down and can set one up quick, and refill even quicker.
Oh..and my juice is mostly PG (85/15) and is clear and thin. My cartos don't flood unless I get juice in the center tube when filling, or I over prime (toking on the carto assembled in the tank without firing the battery). If that happens, I just take the tank/carto off...and gently blow the juice out of the center tube.