Step 4: Washers and PVC
IF YOU WANT TO PAINT THE BOXES, do that before you put the PVC in, because it will be much much much easier. Also, sand sand sand sand the entire thing. I didn't sand the inside bottom, and when compared to the outside bottom, I really wish I did.
I then attached the PVC connector inside the center of the box. I used gorilla glue, but you can also use epoxy or whatever you want to secure it to the wood. try to center the pipe as much as possible.
There really is not too much more to do, but there are different things that can be done to the design.