i have the pro 2 trailer and found i needed more water,rang ionics for advice but was told it was not company policy,something about the danger of carrying extra water in car,went to see local boat mechanic and he was able to put a piece of plastic pipe through the lid into the baffled tank it was then sealed and on top of the lid there is a screw top,similier to a petrol cap,must be screw lid one,when the tank is empty i then get the water cannister out and start to fill,you must use the correct funnel to stop air getting in the tank,the cost was £33 including screw lid,funnel,pipe and the hour works,my advice would be to see your local boat yard mechanic hope this helps.