Just take a soda bottle and drill a hole in the top for a small piece of air hose like you did for your yeast bottle and put some water and liquid detergent in it. Mix it up. Let this soap solution dribble over your battles, hose, and fitting. It will bubble if there is a leak. Just don't let the soap get into your tanks. Your air stone needs to be a new one because they clog easy.
10 gallon hospital tank.
29 & 50 gallon - High Tech C02 enriched.
50 gallon Pond - Natural.