Thank you Alexis!
I've been trying to find details of the wing fuel tank, present on the CHFT variant.
I haven't been able to find any close up photos of the FF.33L with sufficient detail to be of help.
Then it struck me that maybe other Friedrichshafen models may have had the same tank?
In the Windsock album on the FF.33E page 6 top, there is a very clear photo of the tank, at least on some FF.33E's?
Next, at first the bottom of the tank was a mystery to me, but taking a closer look at the many photos
it was quite obvious what is going on...
It looks like there is some kind of 'sump' in the bottom of the tank, that extends to the fuel line.
This is a closeup of the tank on a FF.49, looks a little different, but the same principle.
Cheers: Kent