If you want something cheap and quick use a stainless Turkey baster. The ones with the screw on injector tip is best. Thread on the tip, clip it with side cutters to fit your butane can. Pull the bulb off and add coffee filters and hold em on with a worm drive clamp. Only downside is their limited in size. But if ya fancy the idea i know most Loblaws tend to have em and theyre food grade safe so no machine oil residues
On a side note, they also make glass tubes for this purpose now