I'm an SI gear user and have 4 cartos with the guts ripped out to use for dripping. Their cartos don't have a center tube.. I look right down to the coil top.
To drip, I take the carto off the battery and hold it in a paper towel or tissue.. drip right in.. 3 drops usually unless I'm testing a blend of two flavors.. then it's 4 drops... blow
through the top down to get the extra out and reattach it to my battery..
vape away.