I just double-checked and am definitely using the presta side of the pump and locking it in the right direction. I also tried sanding/cleaning and even the electrical tape but no luck. I did come up with an interim solution. I attached a presta/schrader adapter to the threadless valve so I could use the schrader side of the twinhead pump. Works like a charm! It's a few extra steps but at least it'll get the job done until I'm ready to change the tube. My luck this tube will last forever