First, a labeled picture of the situation:
There are three ends, two in the ground and one in the house. How can I figure out which way the water is flowing?
There are four labeled valves (and one hose bib valve I left unlabeled). I'm guessing C and D are part of the pressure vacuum breaker, but I don't know what any of them are for. What is the purpose of each valve? Turning them all off does not seem to affect water in my house (I only ran water for about 15 seconds). Does that mean water is flowing out of my house at end 2 and into the ground at both ends 1 and 3?
Some additional context: this setup is on the back of my house. I have a pool and an in-ground irrigation system. There is a double check valve in front of my house that I would expect to control my irrigation system, but maybe it only controls the zones in front of my house (I'll be buying a valve handle soon to test it).