The
British standard (BS 7162) for the deck fitting is 1½" ID. The male hose barbs are all 1½". The deck
fitting should not have a chain linking the cap, (you can't
connect a pumpout with a chain in the way), and should be
clearly marked 'Waste." Although the best quality deck
plates are cast stainless steel with stainless steel caps,
colour coded plastic caps, blue for water, red for fuel and
black for sewage are quite suitable and are far less likely
to mistake one deck plate for another.
