Since the connection you describe would be on the intake side of the water pump, will you have a problem with drawing a vacuum on the water maker output line? The pump relies on "sucking the water" out of the tank that is in service, with another line connected at the pump suction it seems that it might interfere with that suction from the in service tank or worse yet, damage the water maker. I would think you could want to have an isolation valve on the water maker output line just before the water pump. Seems it would be better to have the water maker discharge to a tank that is vented but that is just an "uneducated" guess.