You don't have to have the ball valve because the flow rate is really low. If you are going to have a long run of hose, then the ball valve would help control gurgling. I'd put the ball valve at the end of the run though.
I deleted my pm to Richard that had the flow rate. He may have the flow rate. His wet/dry will be next to his tank so he had to use this design. It will not flow as well as the uglier type will flow because the tee is up at the surface. The farther toward the bottom of the tank you can make the tee, the better the overflow will perform. This design requires the tee to be high because the tank will drian to the level of the tee. It keeps the works outside of the tank which looks nice.
I deleted my pm to Richard that had the flow rate. He may have the flow rate. His wet/dry will be next to his tank so he had to use this design. It will not flow as well as the uglier type will flow because the tee is up at the surface. The farther toward the bottom of the tank you can make the tee, the better the overflow will perform. This design requires the tee to be high because the tank will drian to the level of the tee. It keeps the works outside of the tank which looks nice.