Fresh Water All Over
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Since the coach is new to you, I suspect that it may still be winterized. There are low-point drains as well as a fresh water tank drain that exit through the coach's floor. When the fresh water tank is filled, water may exit from any of these points if the valves aren't closed. Your Owners' Manual should indicate where the fresh water tank drain valve can be found as well as the low-point drain valves.
Typically, when all of the low-point drains and fresh water tank drains are closed, water will exit from the vent tube when the fresh water tank is filled.
Good luck with your investigation!
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)