Do not add water through the vent hole on the top of the solar water heater tank.
The water tank of the solar water heater is an “open” water tank. During the water filling process, the air in the water tank should be exhausted through the exhaust hole while adding water. If you add water directly from the exhaust hole, there will be no place for air to escape into the water tank. This will make it impossible to refill the water and easily damage the water tank liner.