Water tank help

Any water tank experts here? Would love some help identifying the inlets/outlets of my old concrete water tank.

Recently moved to a lifestyle property and im trying to understand our water tank. I cleaned rainwater collection pipes that were pretty yuck, thinking it would be taking dirty water to our tank (along with trickle feed), only to discover that this pipe (going from gutters) just went straight into the ground (as shown in pictures- labelled D)?? So now I'm trying to understand what all the pipes/inlets etc are on the tank because I really have no clue.

Can anyone identify A, B, C and D?

Thank you!