RV Repair: Air in water lines, gallon water tank, air in water

Question
Just bought a 2005 tundra 5th wheel.The trailer was still winterized so i started to flush the lines with fresh water and fill the tank. When using the pump can not get rid of air, is there something I'm doing wrong.

Answer
Well there is a six gallon water tank with the water pump it could take up to 5 min to run all the air out. If after that it still does it then I would have to say that 1 not enough water in he tank or 2 water punp diaphragm has a hole in it and is letting the water and air mix on the way in check the water heater by pass and try hooking it up to city water and see if that helps.

If not check back and we con do some different test