Dear Rainer
Many thanks for your reply but I think you misunderstand what I mean !!!
The sanitary device I was refering to seems to be basically a detachable toilet seat which attaches to the top rail, on the sea side, of the railings [is railings the right word?] with two bracing struts leading down a lower horizontal rail or the hull for bracing. It certainly needed bracing because if it collapsed the occupant would likely end up in the sea. The photo I saw also showed a crewman pulling up his trousers standing next to it on the deck. The photo was taken from the top of the conning tower looking slightly forard. The man in the pic was looking at what he was doing pulling his 'patchen' [is that the right word?] trousers up and looked like he was unaware of the photographer.
This device must have been detachable and stowable [where?]. When was this contraption used and why? I guess if the boats deck was awash they could have used the deck gun ammunition chute which ran down through the tower wall. Although later when deck guns were mainly removed they might have also removed or sealed this ammunition supply chute.
Also what happened to the horseshoe shaped life preserver (belt) which is or was usually stowed in a bracket on the [port?] side of the conning tower as I have seen a [contemporary] film of the tower watch going below as in an 'alarm' dive and the last thing the last man did was to take this horseshoe shaped life preserver down the hatch with him - they had it loose by the scopes on the tower. As I saw, the four lookouts dived down the hatch, then the fifth man [watch officer?] grabbed this life preserver and shot [yes thats the right word] down the hatch in double quick time.

Best regards,
Harvey