you have to take the brass fitting out and then pierce the film below it and set the brass back in w/o leaking or silicone it in. The butane spout in the can needs to have a V notch in it to refill
1)Take the butane cartridge out of the thermacell.
2) With a pair of pliers, gently rock the metal nipple ( careful not to damage the o-ring on the nipple ) from the cartridge.
3) CAREFULLY use a small wire ( I've used things like a paper clip, small straightened fish hook and wire leader material ) and push it into the mouth of the butane cartridge. There is a very small, white gasket-like membrane you need to pull out. This is the trickiest part of the refill process and you'll screw-up a few times before you get the feel of it.
4) Butane refill cylinder. Buy it any hardware or camping store. Cut the tip at an angle / and turn the Thermacell empty cartridge upside down. Insert the refill cylinder into the cartridge and fill to about 2/3 allowing for expansion.
5) Remove the refill cylinder from the now 2/3 full Thermacell cartridge. Reinsert the metal nipple into the cartridge and tap it back in with a hammer or pop-it with a piece of wood.
As for the pads..... Thermacell uses Allethrin, which is a synthetic copy of Pyrethrin. Pyrethrin is a naturally occuring insecticide made from chrysanthemums. There are many different products that are Pyrethrin based. I've used a fly spray for horses and a non-toxic spray for plants that have pyrethrin in them. My best results have been from spraying the pad with a few squirts, letting dry (crystallizes ) and reapplying one more time. Keep the pads in a ziplock bag and use within the month.