No water at sink when using internal pump/tank

[RichHog]

Just got back from camping in Colorado and didn't have any water at site. So we filled the fresh water tank and turned on the pump. It whirled, gurgled and we had water in the back bath faucet (hot and Cold) and plenty in the toilet. I had also put a cap on the inlet connection as I suspected a problem with the inlet regulator. Sink water both hot and cold just gurgled and didn't flow. It works fine when I am connected with a hose. Tried changing valves under the sink but didn't work any better. Any thoughts? Also isn't the pump supposed to come on and off as it is needed once switched on? It ran continously once switched on at the panel? 72 Tradewind.