I would go with a couple of the less expensive, yet quality, cartotanks to see if they fit your vape style. I'll provide two examples that would be good for an ego battery.
The 3.5 ml polypropylene DCT tank kit from My Vapor Store.
510 Pro DCTank Combo
For under $22 you get a complete tank kit, including the tube, metal endcaps, drip tip, and your choice of 5 cartomizers that already have holes for use in a tank. You'll be offered to choose between single or dual coils, the resistance (ohm rating), and the number of holes in the cartos. You can also choose between a clear or color-tinted tube. These tanks are safe to use with all flavors of e-juice, immune from cracking with flavors like cinnamon.
For an eGo, I'd choose the 3.5 ml version, with 2.0 ohm single coil cartos with 1 or 2 holes, depending upon the pg/vg ratio of your juices. If you use juice that is more than 50% vg, get the 2 hole. Otherwise the single hole will work fine.


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A little nicer option is a pyrex tank from
IBTanked - Get Tanked With Us! $25 will get you a clear pyrex tube and stainless steel endcaps, a pre-punched carto, and a combination drip-tip and tank-filling tool. Additional cartomizers and a selection of drips tips are also available on the website. The slimmer 19mm tank is more appropriate for a slim ego battery.
https://www.ibtanked.com/kits/complete-tanks/19mm-clear-tank-detail


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You may wish to find an eGo cone cover like the one pictured below from an online vendor. This will hide the space between the tank and your eGo at the connection, and also provides additional support for the tank.
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Just an aside note concerning the pyrex tanks from Valley View Vapes. They are excellent tanks, but be aware that they are 1" in diameter (25mm) and will look quite top-heavy on an eGo battery. Just a heads up if aesthetics are a concern.
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