blowout

I want to blowout my sprinkler system using air compressor but was wondering if I should use the test cocks or the hose outlet. I'm leaning towards using test cock #2 - which means I'll need to remove it and need a nipple and coupler to attach a air hose. Is this a good idea? If not, what...

I'm looking to do a blowout in the new home that has the Wilkins backflow preventer. Everything I read says that it shouldn't blowout through the BFP. However when I look at where the compressor can be connected it seems that the air will go through the BFP. See attached picture. This is an...