I put the hole at the bottom in the picture to show what scopus tang was talking about. He said that if you wanted to do a quick water change, you could, by merely twisting the pvc pipe to the right and having the water drain into a 5 gallon bucket for waste.
The idea of having a ball valve is to control the amount of flow in your tank. It's not always best to have resistance on your pumps, because it can shorten the life of them and create excess heat in your tank.
I have six 30 gallon tanks that have two 1" bulkheads in the back near the top. They work perfectly.