My friend had a water leak from the main cold tank which we fixed by replacing the float valve (ball cock). What is mysterious is that the tank leaked so he had a dripping ceiling. There was no water out of the overflow which appears to have an elbow bending into the water and a little canister just outside the tank in the overflow run. Something called a Bylaw 30 overflow kit. We poured water into the overflow by turning the elbow upwards and it worked ok - water came out of the overflow pipe poking out of the eves. Is this type of overflow liable not to work ? Some sort of airlock ?