I believe your correct in assuming the converter would supply the power to the water pump if present.
The only time I ever heard the water pump in my RVs was when it was on and water was being used some place in the RV. (sink, shower, toliet ...)
Having water in the "Fresh" tank, then turning the pump power on, and opening a faucet should engauge the pump.
My Other House Is A '02 Jayco 31FKS Designer TT