goes without saying to make sure to turn the water off to it first and set it to pilot. Just twist that and it will open. I agree with connecting a garden hose to it so it doesn't spill everywhere.
Also if you get no flow you might need to hold open the pressure release valve near the top of the tank to let some air in.
2006 Edmonton Indy - Heatstroke
2007 Vegas Grand Prix - Fremont awesomeness
2010 Montreal Grand Prix - Section 11!
2011 Edmonton Indy - Mudfest
2012 Nascar Autoclub 400 - Convinced I attract rain....
2016 Spa & Monza. Ya baby!