Margie, plastic or metal style tank? Please keep in mind that the plastic style tanks have to 'click' in place(the Carto has to be swirled in a certain way for it to be flush and sealed with the bottom of the tank).
It's possible its the O Ring, but unlikely since its new. It's also good to kind of 'lube up' a new Carto before shoving it up in the tank lol, the dryness may cause damage from forcing it.
Has he tried a different Carto? It's also possible he burned the middle of the Carto, I believe they refer to it as a 'wick'. Once/if you burn a hole in it, your Carto is done, it will leak. The prevention for this is to NOT let your Carto dry out, it will start burning the polyfill inside and ultimately ruin the Carto.
Practice good filling techniques, and basically, practice makes perfect. We all start somewhere, and learn from our mistakes.
I hope this helped, if any other questions, feel free. I'm not good with tech-inclined inquiries, like voltage and wattage, etc... But I have a bit of experience under my belt
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