I have now found that at least one of the fittings on top of one of my fresh water tanks is leaking. Probably a cracked elbow. Why is there two of these plastic fittings on the top of the tanks? Can they be repaired or replaced? Do they just unscrew from the plastic tank? Btw, While I have the tank down I am going to add extra metal bars for supporting the tank as I read in another post. Thanks.