For the methane bubbles, I just attach a 10 mm rubber tubing from the natural gas jet on the demo table to a bubble blowing trumpet. Do NOT use propane nor butane, they are denser than air and will sink instead of rise.
I dip the trumpet into a dish of bubble soap made from about 100 mL of JOY detergent dissolved into a half-liter of water. Add a few mL of Glycerin. Shake it up and let it age for while.
This blows about one-liter sized bubbles when the trumpet is held sideways as in the photo above. You may wish to try different orientations.
Then, with pith helmet and goggles, I have students ignite the bubbles with a 50 cm wood splint as they rise up about one-meter above the horn.
Here is where you may purchase a bubble trumpet:
Good luck, and have fun!