I find that sucking the flower up and in is too much. The pax loading scoop works perfect for the glass stems. I can just lightly get it full to what ever level and barely use the flat end of the tool to gently just square off the top of the load. Just so I get an even height layer of the flower and keep a little open gap till the end. I also stir the load at some point, maybe 1 or 2 times per load. With some strains you may get more build up in the holes obviously....as well as moisture content being a possible issue as well. This is why I use a screen. I can clean it quickly with a pic afterwards and just blow out anything else. I usually then clean the screen and stem out after about 4-6 sessions. It keeps decent air flow this way for me. Also I use the WPA's and not sure if they are aftermarket stock stems with a welded on WPA joint...or fully custom stems with possible difference in hole sizes from stock stems. I thought at one point one of the two WPA's I got (from PUI and S-Pete), had slightly better air flow and maybe better than the stock stems. I would love to see a more open glass screen/hole area on these stems. But I did not find it an issue at all for direct drawing use. And I am used to arizers......and I find this fairly easy to draw on without tiring my wind bags out like other session vapes. I even put a small piece of organic cotton in the stem to see what the difference in taste/smoothness is. Then the draw resistance was an issue.....with only the smallest amount of cotton to stop any tiny bits.