Marco,

I have A Zone VI 16x20 washer that I have used with 16x20 prints for many years. While the dividers in mine are 14 inches high it has never presented a problem. The spouts are on the top of the input chamber and the water flows out (down) into the opposite side chamber and out of the washer through a hose on the top of that chamber. The bottom opening of the hose is 17 inches. There is also a drain hose at the bottom of the exit chamber so the washer can be emptied. I don't recall when I bought it but it has been quite some time ago and was purchased new.

http://www.jeffreyglasser.com/