I own one of the Vicks cool air units and have not used it for a couple of years. I tried to put water into the tank which has a handle on top and the top would not come off, no matter what I did. So I just put the water in the base of the unit which works fine. However, I do not have the owners manual any more and would like to know proper care and handling of this unit. I do not see any serial number or model number on the unit. Can you help?