We have the system that you are looking for the Pentek 20" x 4.5" big Clear System. The Penek #20 Big Clear Whole House Water Filter System had a clear sump and a white cap with a pressure relief button. The 20 inch big clear system by Pentek can be found here:
http://www.waterfilters.net/Big-Clea...g_p_0-575.html
The Pentek 20 inch clear system will fit the full selection of 20" x 4.5" replacement water filters that can be found here:
http://www.waterfilters.net/culligan...h-Big-Blue.htm