I'm a new kegger. I had a 4 gallon batch of beer bottled for about three weeks, and when I tested it, it was flat. Not sure of the reason; it was bulk primed, had two weeks of fermenting in the bottle and a week to cool. So, I poured the beer in a keg, sealed the keg with 30psi, and set the pressure back to 12 psi. 5 days later, I am getting a mixture of gas and beer coming out of the tap. Suggestions?