This is what I do, and I don't know if this is the best way or even makes a difference but I have not had a burnt Carto yet.
I fill my tank and then start with the carto. Tilt at an angle and put 9 or so drops in. I then draw on iit 2 times as if I were taking a hit then I do the 9 drop thing again. As ur filling the carto turn it a little after each drop so u saturate the batting....I repeat this at least 3 times.... it will look slushie as u first drop it in but after a minute or so it dries at the top...also the thicker the
juice the longer it takes to get the bottom saturated. Sometimes its a 30 minute process cause I will let it sit a few minutes then put more drops in for good measure. I prime mine and hubbys
tanks and have not burnt one yet.....hope this helps/makez sense.