Your talking about the DefCon, right? if not stop reading here... There are 2 tiny holes in the silicone cap, off to either side. The same cap that has the hole for the wick. Those 2 tiny holes are needle holes from which that silicone cap was originally intended for use. The cap is repurposed for use in the DC. So, if you take a sharp needle you can very easily enter the tank thru one of those holes. Just be sure not to push the cap down or you will have a disaster on your hands. I have not tried this, but I have owned and used the original product that those silicone caps come from, and that is the only way to fill the original product, thru those 2 tiny holes. Again, I have not tried this, attempt at your own risk. I would not tell you this if I didn't think it would work. I def would not try it w a blunt tip needle you will for sure push the cap down. Good luck.
Last I checked I didn't see any other holes in the cap, but I'll look again. Thanks for the tip!