Ronco Marine Holding Tanks All Sales Final on Ronco Marine & RV Tanks.Our Marine Holding Tanks are manufactured with polyethylene resin that meets Coast Guard Standards. Our Marine Holding tanks come complete with:NPT threaded openings and adapt easily to any boat. Marine Holding tanks come with 2-1 1/2" fittings and 1-1/2" vent . (Except where noted *) Marine holding tanks that have a (*) do not come with fittings. Order the Easy to install fitting relocation kit. +Tanks without drawings next to the product description are rectangular as show above Marine Holding tanks come with 2-1 1/2" fittings and 1-1/2" vent. (Except where noted *) Trionic Marine Holding Tanks TRIONIC offers an extensive line of Marine and RV water and holding tanks to meet most size and durability requirements. All tanks are rotationally molded of a seamless one piece, non-corrosive linear polyethylene that meets FDA acceptance and complies with Coast Guard regulations. Each holding tank has one 1/2" vent and has two 1-1/2" openings. Openings on all tanks are female National Pipe Threads (NPT) and are located on one end of the tank. We offer custom fitting locations. All of our tanks are guaranteed to be extremely durable and will not collapse when emptied with high capacity pumps. Tanks ordered with custom fittings cannot be cancelled and are non-returnable Todd Marine Water/Holding Tanks Todd’s one piece molded Water/Holding Tanks are tough and durable. Each tank fully complies with FDA regulation CFR 177.1520. All Water / Holding Tanks satisfy all United States Coast Guard standards. Polyethylene tanks will not emit waste odors or change the taste of fresh potable water. All openings are female NPT (National Pipe Threads) and are located in the same relative position on one end of the tank. Fitting Sizes: (2) 1/2" and (2) 1-1/2" female NPT fittings Click here for Uniseal Slip Fittings - The easy way to install the size fitting you need, where you need them! Click here for Holding Tanks Kit Fittings(Threaded Fittings) - The easy way to install the size fitting you need, where you need them! *click here--for tank installation guidelines.