Welcome to the world of Vintage Airstream ownership!
The valves that you are seeing on the water supply lines are likely low point drains that are utilized when winterizing -- there likely will be one for the hot water lline, cold water line, and water filter line below the kitchen sink. The. Rear compartment likely has hot. And cold low point drains for the sink and bathtub as well as one for the toilet line. You will also likely find one or two low point drains near the water heater. You will also likely find drain tubes through the belly pan for the air conditioner condensate drain and a drain tube for the fresh water tank.
Good luck with your Airstream.
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)