Building my 1st serious rig. May I use push to connect fittings?

Depends on what stage of the regulator you are talking about.

I use stainless push-connect couplings to connect the 20lb low pressure from the tank to the solenoid/needle valve, no problem.

I would not use push-connect on the high pressure side-too dangerous.

I used a black high pressure flex hose for years but recently bought cheap regulators to reduce the pressure and then feed the reduced pressure to the victor, making it a secondary regulator.

As with any connection, check for leaks. I found it best to use kid's bubble solution instead of soapy water because it has glycerin in it and makes for smaller more detectable bubbles. Apply with a small paint brush (the kind found in kids water paint kit). Both of these are found in the toy department in walgreens.

 

Yes, check the brand for PSI maximums. Recommend Parker Legris push-connects over any other brand because it's smoother to insert tubing as easier to get them off.