These are the three through-hull fittings that link the toilet and wash basin to the sea. They are supposed to be shiny and clean.
When I tried to remove the smallest it turns out to be brass. Now brass is an alloy very rich in zinc and this corrodes away in seawater through electrolysis called de-zincivisation. Only the zinc disappears so the metal becomes very weak. I tapped it with a spanner (as you do) and it crumbled into pieces. The pink colour is the brass after zinc loss.
So three new sea-cocks at £150 each! Yuk.