I have a difficult time filling the water storage tank on my 05 Forest River MB Cruiser. The water goes in OK for a short time and then the tank backs-up out of the inlet and "burps" out some air. After the "burp" I can fill it again briefly but the same thing happens. It seems like the storage tank is not vented properly. Is there a vent that needs to be opened when filling the storage tank? Has anybody else experienced and solved this problem?