The trick that Tiger4x4RV said works fantastically. My wife and I had run our "Band Boosters" football game concession stand for several years when my kids were involved in HS Marching Band. We had two 100# tanks outside and pouring hot water on the side told the tale. We had no auto-switch over regulator and couldn't afford to run a tank out during the half time rush, so we checked using that method before every game.