One should go to the top, the other 2 should go to the bottom, a couple of ways to do the bottom 2.
1. both have a tube and weight (called a clunk) that go all the way to the back of the tank but not touching the back (it needs to be able to move to the top of the tank when you are flying upside down. With this setup either of the 2 will go to the carb or use for fueling.
2. only one has a line and clunk and the other has a tube angle to near the bottom front of the tank. In this setup the one with the line and clunk goes to the carb, the tube angled down is for fueling.
The line going to the top of the tank goes to the muffler.
ALL that said with a tower trainer you don't need a 3 line setup, that is for a coweled engine. I would eliminate one of the bottom lines.
When fueling pull the line off the carb and fuel.(it is ok to pull the line off the muffler also while fueling so when the tank gets full it will not pump fuel into your muffler)