You just add butane to the bottle? Does it sit on top or go to the bottom?
Tetenal sells a protection aerosol in a can. It's Propane and iso-butane, these gases can be, with a tube, forcefully displace air in the ullage of the container. I have used a small butane torch. Don't use a lighter, if you hit the igniter, it's a bad day.
Back when the US-EPA only worried about ozone and not global warming, you could buy aerosol dusters that used HFC-134a, these worked great. Now 134a and most HFC (s) are banned in the US, Canada, EU. China still uses HFC 's, HCFC 's and (by bribing the right official ) CFC 's. Freon 11 is the greatest foam blowing agent ever made, spray foam for building insulation is a huge, enormous, industry in China . So you either leave no air or adapt which means using a flammable compound. All domestic, home, refrigerator freezers are being converted to iso-butane for refrigerant. This is what is used in disposable cigarette lighters. It's been used in the EU for years, decades in Germany. There have been a couple explosions but under extraordinary circumstances.
So, yes, you add butane to the bottle. Or easy use a small bottle and fill it to the brim, this is what I do with black and white stock solutions. If you exclude the air, all the air, you can, keep print and film developers for a couple years. My record, believe it or not. When we moved, I found a bottle of XTOL stock solution, 11 YEARS OLD, in a flimsy PET soda bottle, I had squeezed all the air out. The XTOL looked like crappy American beer, like Piss. I was getting ready to toss. I thought I may never get another chance.,I developed a roll of 120 TMY-2, extended the development time by about 50%, the negatives look great. There's an old thread here on it.
Air burns down houses, does the same thing to developers (and sometimes fixer).