Well, I just uploaded some pics for all you tank and cell geeks.
(I hope imgur doesn't screw up the quality, each scan is about 8Mb in size)
Pic 1 shows where the
valves for the diving tank 2 and 4 are located (Entlüftungsventil Tauchbunker 2 + 4, bb = port) - you see a corresponding valve on the starboard side, too.
Pic 2 shows the location of all central-located tanks
Pic 3 shows shows that my previous assumption about the air pipe to the Diesel engine was wrong - you can see the pipe only branches to the engine room and the kitchen.
All drawings depict a 1944 type VII C
Source: Eberhard Rössler: Geschichte des deutschen U-Bootbaus, Band 1 - isbn: 3-86047-153-8