15:44 Jan 5, 2011 

I hardly think "submerged" is necessary - any more than plongueuse - in the case of the suction pipe. If the pipe were not de facto submerged, it would be impossible to withdraw our precious hydrocarbons from the tank once the level dropped below the bottom end of the pipe.

"Submerged/plongeuse" is really only necessary in the case of fill pipes. Service-station tanks are filled from the bottom (from below the surface of the liquid they contain) to prevent causing explosive fuel vapour. De facto they NEED NOT be submerged since you can fill any tank from the top; they are only DE JURE submerged, so it is deemed necessary to specify.