u,
I have the same question as Jimmy... in the Drop box 3 pic, at the bottom right side of your valves, it looks as if the pipe is capped off. It could just be a 'T' and the pipe continues into the ground but we can't tell.
Assuming that all the pipes are working, you have three inputs to your pump... Most likely, from the Skimmer, Vacuum, and Main Drain.. In your pic, all three are open... Unfortunately, no one here can tell you for sure which pipe goes where.. You just need to experiment with each one.. Set the valves so that only one pipe is open at a time and see if you can tell where the water is coming from... It should be very easy to do this with the skimmer and the VAC line... That means that the other pipe is most likely going to the main drain...
Play with it and see what you get... Just make sure to keep an eye on the pump.. If the VAC line is not open in the pool end or the main drain has been capped off, then the pump will very quickly run out of water.. Do not let it run that way for more than 10 seconds or so..
Thanks for posting,
Jim R.