I had trouble with the original design during a heavy rainfall. The mosquito screens (shown below) are 18 X 18 mesh and tend to load up in a heavy rainfall. This caused a vacuum lock in the downpipe and the leaf deflector would overflow. The two inch tube on the left in the new design allow air to enter below the screen and acts as a vacuum breaker. The four inch fitting on the top of the air vent also contains a mosquito screen.
I found these 4.120 inch stainless steel screen on eBay. They fit perfectly in a 4 inch PVC coupling. The large screen on the tapered section of the leaf deflector is quarter inch galvanized hardware cloth.