Abstract: An integrated plumbing system comprising a plurality of interchangeable and interengagable parts which is especially useful in conjunction with boats or other marine vessels. The plumbing system includes a through-hull unit, a mounting unit, a ball valve and a plurality of components useful therewith. The components, including the valve, are made of a strong, non-corrosive, non-metallic material, in particular, a plastic-type material known as MARELON. The valve and associated components and fittings provide various configurations of units which are adapted to numerous plumbing requirements. The mounting unit permits close-coupling of the system to provide enhanced lever ratios in the event accidental side loads are applied to the system.