Thanks for all your replies. Bruce K’s description is pretty much spot on. My boat is from round about 1970ish and I’m assuming it was original fit.
The lever on the right operates a flap-type valve, directly through a very short vertical pipe through the
hull. No other piping involved.
Method of operation is...
1. With lid closed, briefly
lift lever on right to let a little
water in.
2. Lift lid and do necessary
3. Close and clip down lid
4. Lift lever and swiftly push down dome, ensuring small hole in black top handle is covered.
5. Release lever and pull dome up.
Really simple and would be easy to clear if it ever blocked. Only disadvantage is it’s not suitable for inshore, harbours,
anchorages etc.
Wondering how ‘safe’ it is and whether I should replace it.