You are probably gonna have to experiment some to use Boba's Bounty in a cart/tank. I've heard reviewers say this is the thickest juice they have ever used.
I think I would try to dilute the Boba's with some distilled water. I can't tell you exactly how much, but perhaps as much as 1/2 ml per 5 ml juice. Boba's is a relatively strong flavor and I don't believe you will notice the dilution in a carto/tank. I didn't.
I have some Boba's in a Smoktech dual coil tank, with two self-punched holes opposite each other. It's still a stiff pull even after I've diluted it with some water. I haven't had any issues with flooding. I have a hunch that you have been drawing so hard to get the thick juice to the coils, you are flooding it. This juice requires a slower, gentler, and longer draw in my opinion, it's so darn thick.
I have noticed if I do a pull without burning, while exposing one of the holes to the air inside the tank, I seem to get better juice delivery to the coils and a nicer hit. So I'm thinking it has something to do with the pressure inside the tank. I think when I replace this carto, I will still use two holes, but with the first hole low as usual and the second hole higher on the carto (upper middle on the opposite side of the first hole) to help pressurize the inside of the tank - just another idea for you.
My next suggestion would be to start over, again. New carto. Empty the juice that's now in your tank into a small container for the time being.
Carefully prep a new punched carto. Stick a toothpic into the air chamber to ensure no juice gets in there while filling the carto. Take your time with Boba's, esp if your polyfill is tight (ie Boge's). When the polyfill looks like a slushy, you're done. Hopefully you have a tank filling tool; replace the toothpic with the tank tool, if not leave it in the carto and insert the carto partially into the tank and fill it up. Then insert the carto fully into the tank, and remove the tank tool or toothpic, and add your tip.
These are just some suggestions thrown into the wind for you to ponder. Boba's is not one of my favorite flavors, but I keep picking it up occasionally, hoping it will grow more on me. And it has to a point, but I still tire of it after a few minutes.