I can't seem to connect red or green wire to fluid depot to see how much liquid is store. I can do that with normal depot. Am I missing something?

i would like that function too, for fuel depots as well as for liquid provider depots, but it seems to be not implemented (maybe impossible to do? or just forgotten to enable, similar to how normal depots also at first couldn't be connected by wire). in the meantime, i use a setup of pipe->pump->tank->(optional second pump)->depot and thus can read the tank whether fuel has filled the depot, and even switch the first pump off to not unnecessarily fill the tank completely.

I was just going to suggest the same thing.

I added circuit readers and writers, use them to read the contents