Marvin said: There should be a shutoff valve at the bottom and top of a sight glass. The upper attachment point for a sight glass is never right at the top of the tank--- it's always an inch or two or more lower. If the tank is full and there is no closed valve at the top of the tube, and if the tube splits or starts to leak, all the fuel in the tank down to the level of the upper sight tube attachment will leak out of the tube into the bilge and may get pumped overboard by the bilge pump. In the case of a large tank, this could be many gallons of fuel. Marvin, have you checked fuel prices? Unless you're getting a never to be repeated great fuel price or venturing out on an around the world journey, most would be lucky to carry half full fuel tanks :-) FWIW, I leave the top valves open and the bottom closed. The rationale is to totally eliminate any pressure on the sight glass tube that looks like clear water tubing. Gil _____________________________________________________________________________ _______ Do you Yahoo!? Everyone is raving about the all-new Yahoo! Mail beta. http://new.mail.yahoo.com