Haha....I haven't had any problems getting the tube off...so I'll have to defer to Rob on that one. The tube isn't as hard to get back on as you might think. ....but may take a few tries. Simply use a few drops of VG or PG or your ejuice to lubricate the end that goes on the nipple, pinch in the tube between your thumb and forefinger and gently twist the tube onto the nipple. 
