Turn the water on and see what happens! The downside is that any leaks you find should be fixed in order to see other leaks down stream. Best case scenario: Your mainline and valves hold and operate, allowing you to operate each individual zone. I'm assuming you have a valve setup on the side of your house in which the zone valves are above ground level?
Most anti-siphon valves have a manual on/off setting just below the valve selonoid. If the mainline holds, turn the on/off until you hear water flushing through the valve. Then, go and check where the water is going.
It gets tricky if you run into a lot of problems with this system. Problems can quickly add expense to a system that may not even be up to standard. I suggest being careful as to the amt. of money spent on repairs to a DIY system. I've seen some bad ones in my day, and have suggested numerous times that a homeowner is money ahead disregarding the old system and installing a properly designed new one. Too many times have I spent hours fixing leaks and repairing valves just to find out that the system is under-pressured or heads are spaced too far apart. All of which can be fixed, but would cost the same as a new system with a 5 year warranty.
With that said, some components like the controller and heads could be reused. A controller can easily be tested by using a multimeter to determine if it will put out the power to each zone. Plug it in and run it as if the system were useable. See if it does anything "squirrely" and check to see that each zone puts out the 24-26V it should.
As for flushing out the system, once the system is operational, unscrew the last head of each zone and run the water through each individual zone one at a time. I try to start with zones closest to the water source and work my way out.
This post has been edited 1 times, last edit by "Central Irrigation" (Mar 3rd 2011, 2:57pm)