When I used to blow out the lines I was told no more than 35 psi. Mike, blowing out the lines is an option to the antifreeze rather than a supplement, although you could do both if you want. Some are not comfortable that blowing out the lines really gets all the water out. Others don't worry about it.
Re the checkvalve, you can push the pin or just remove the hose from the valve if you can get to it on the inside. Twice I had the o-ring pushed out of place when the checkvalve froze because I'd not release the pressurized water at the valve. Once I was able to work the o-ring back in place. The other time I had to replace the city water assembly. This was when using antifreeze. I did not have to worry about this when I used air pressure because the air fitting connected to the city water inlet and cleared that checkvalve by default.
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