If you blow out your hoses you will be violating the law. 134 hoses have the adapters that seal the hoses to prevent leakage to the atmosphere. To be legal you must have valves at the end of your 12 hoses for the same reason.
Blowing out the hoses is considered venting and is a violation of FEDERAL law.
I know, I know someone will ask how they will ever be caught doing this. I don't care if you do it or not, it's your business. I just want to make sure you know that you are violating FEDERAL law.
I will not do this because my gauge sets are used with my recovery machines. If I used the same gauge set on both machines I risk contaminating recovered refrigerant.
Have a great day,