Something to do with partialy used gas canisters.

That’s why the G-Works Gas Saver caught my eye. It’s a two-way isobutane canister adapter that lets you transfer the gas from one isobutane canister to another so you can refill partially used or empty canisters

Is the G Works Gas Saver worth buying? While it provides a way to transfer unused gas between canisters, it takes a fair amount of time and fiddling to get the job done. I honestly can’t see this becoming a big consumer hit and I doubt any of the existing canister or stove manufacturers will champion it, though time will tell. While the G Works Gas saver does reduce canister waste, there are easier ways to accomplish this by switching to another backpacking fuel source such as alcohol, white gas, wood, or esbit cubes, which are unencumbered by fixed size containers.