(hydrogen peroxide) fill and drain valve.
Picture 2 of 3.
A hose from the hydrogen peroxide servicing truck would attach here to fill the
hydrogen peroxide tank and (for Mercury-Redstone flights) the auxiliary peroxide tank.
Another hose would attach to the hydrogen
peroxide overflow and vent port, located on the end frame next to the
steam vent, and connect to the truck's H2O2
overflow tank (basically an enclosed bucket).
Overflow hydrogen peroxide was diluted and discarded, due to the possibility of
hydrogen peroxide required special handling procedures (personnel who handled
hydrogen peroxide wore protective clothing consisting of boots, flame-proof
coveralls, a face shield, and gloves) and any contamination would make the
peroxide dangerous to handle.