Inside it there is a gasket, that is, a ring of smaller diameter (about 2 cm) with a cloth on it, preferably one that does not rot. I use fleece. The ring wrapped in fleece is located approximately in the middle of a large tube. You can arrange the ring in the tube using a long tube of smaller diameter.
Then pour a little gasoline for cigarette lighters into the tube; it mustn't drip from there, you can even shake the tube a little. Such kind of gasoline can be purchased at any store selling lighters. Then dip your hand and the tube into the bubble solution, inflate a bubble and you can set it on fire. Due to the fact that the tube contains gasoline vapor, your bubble burns. This is a kind of DIY apparatus for fiery bubbles (Props, Fiery Froth Tube