I had tried a couple of the Smoktech clear polycarbonate tanks with black end caps. I did the carto prefill method, inserted into the tank, let it set a few minutes, and vaped. One leaked from the top endcap (poorly fitting upper tank cylinder) and another carto flooded and leaked at the battery connection. Threw them away.
I got one of these
510 Pro DCTank Combo and did the above juice fill routine. Worked like a charm...great draw, vapor, and flavor. Ordered a few more, same great results. These tanks have metal endcaps and a polypropylene (syringe plastic) casing, which to me are more superior materials for a cheaper line of tanks. These tanks are solid and don't leak. I've been using these for about a month and love them. I have several colors with different colored Cherry Vape ming style tips to differentiate my favorite juices.
I do believe you need to pre-fill the cartos before putting into the tank, or alternately fill the tank and then fill the carto once it is in the tank. I also will occassionally top off the carto by simply taking off the drip tip and adding juice until I see the fill is moist.
My method of vaping with tanks is to use multiple short sucks with each vape. You may need to choose how many holes to punch in each carto depending on the thickness of your juice. I've had luck with both single and triple punched cartos, my favorite is the triple.
Note if you get the above recommended tanks/cartos, choose the proper ohm for the device that you use (3.7 or 5+). Don't give up, once you find what works its the best, convenient way I have found to vape.