Jukka, et al:

The U.S. fleet boats had two sanitary tanks.
No. 1 had a capacity of 434 gallons and was located inside No. 1 Main Ballast
Tank (Fwd. Torpedo Room) connected to the officer's head. It had a single stool
and was blown usually on the 4 to 8 watch daily, surfaced or submerged.

No. 2 had a capacity of 673 gallons and was located inside the pressure hull in
the after end of starboard end of the After Battery Compartment, and was connected to the crews head. Two stools were available and it too was usuually blown on the 4 to 8 watch daily, surfaced or submerged. The waste from the galley and washbasins and showers from the crew's head went into No.2 sanitary tank.

Charcoal filters were installed on the vent lines for use when blowing the tank inboard while submerged.

There was also an "air-expulsion" head (No. 3) in the After Torpedo Room containing a single stool. Special operating instructions were permanently posted inside the head. This head was named the "freckle maker." There was no sanitary
tank; just enough room for single usage and blow it overboard after each use.

Hope this helps,

ROBERT M.