I haven't bought a Protank yet, was waiting to hear the reviews. Didn't surprise me that there are leaking and flooding issues. I heard so much about the Kanger T-3s that I ordered a bunch. I have had the same problem. They're great in that they hold 3ml, but I've had them flood worse on Ego Twists than my mods. I have to turn the voltage way back to 3.2 or it gets too hot for the bottom coil. It doesn't do that on my mods. I've tried the upside down, blow out, etc and sometimes it works, and sometimes it doesn't. If I have to do that a few times, I end up losing a couple of ml of juice, which doesn't please me.
Because I vape darker juices, I pretty much have to soak them in vodka every 2 days or they start gurgling, then leaking, then flooding. So I've bought a dozen replacement coil heads. I think they are high maintenance for the value that you get in holding more juice. I don't want a big tank on an Ego. I've got an Artemas (small & large), Vape Only and 5ml Vivi Nova that are fine for mods. But I like to switch out flavors a lot and usually have about 10 or 12 going at the same time so I have variety.
I have a few mini Vivi Novas and by golly, they don't leak, but I don't get the flavor and it's a tight draw compared to Stardusts or T3s. I would sure like the answer to this question too.