As lllesheim71 said, the check valve in the flush port is stuck open with debris or corrosion/salt buildup. It will need to be removed and cleaned. A grommet and seal may need to be replaced. As long as they can get the water jacket cover off, it is not a difficult job. The bolts tend to breakoff.
Do not use it with the water coming out of the port. It is possible for the engine to overheat. If you have to use it before you take it in, plug up the port. Use a pipe plug in the port or remove the hose from the flush fitting port and plug the end of the hose with a bolt and a hose clamp.
Mike