During a pre-trip inspection of an air-braked heavy vehicle, what is the correct method to locate small air leaks at glad-hand couplings, hoses, and valve fittings?

1. Passing an open flame along the hoses to heat-seal the leaks
2. Listening for hissing with the system pressurized and applying a soapy-water solution to couplings and fittings to watch for growing bubbles
3. Spraying the fittings with ether cold-start fluid
4. Wrapping every coupling in adhesive tape as a permanent repair