Avoiding Pressure Loss

Not off to a very good start, assembled the pressure reducer, backflow preventer, two water filters, drain valve and a couple of valves. Slapped it up and one of the valves is leaking, you know how there is a nut on one side that is part of the valve body and a very fine seam. It's leaking from that seam...... There is probably one in a thousand or ten thousand and I win the lottery.