classic33
Leg End Member
If the valve relied on water holding it shut, wouldn't it be a simple pressure release valve.Trouble is, the hatch being on the outside, the tide would tend to close it and hold it shut, and when the water goes back out again, the hatch would open outwards. Also, the figures are marked on the outside, so it would be hard to equate them with a water level inside...
But yes it is taller than what shows, and there is one remaining tie attached, with fittings for two more.
Given that it was tied into the sewage system, with the tide in, holding it shut preventing any sewage leaving the system until the tide receded, taking the sewage with it.