Jewelers files are very small files. I leave the condoms on, slide down the lower one, mark the place I want to file, and then use the edge of a flat file to make the slot. The slot I come up with is about 3/16 to a 1/4 long in circumference. I use one of the oval shaped files to clean up the edges so they are not sharp. This would tear up lower o-ring, if I didn't. Even then, on a Phiniac tank, I have to punch or drill. The o-rings on a Phiniac tank are so tight, the slot still damages o-rings. They don't on other tanks.
This slotting works for me with any kind of juice. I have used 100/0, 70/30, 55/50 and 20/80. I don't get any flooding.
Here is a picture of the kind of files I use.
View attachment 238699
I use the condom method for filling. I only use XL 2.2 boge carto. It takes about three 3/4 full long condoms to fill an XL carto. After the juice bubbles over the top of the center tube, I add a little air pressure to the top of the carto. This forces the juice back down into the filler. I do this thru three 3/4 fills on the condom. When it starts to come out the slot, I know I am close to having a fully primed carto. I hold my finger over the slot to get the juice past it. Always works for me.
Greg W.