After my second "plastic vented loop" the second time I went manual. I literally mounted a 1/8" ball valve at the vent and it worked as well as I worked it for a few years. When I replumbed I went to a bronze unit mounted higher in the boat.
This was early in my A-4 experience and I used it for about 5~6 years.. Forgot once on the back side of Catalina
. I sucked the water off the bottom and was on my way. I did change the oil when I got back to port and it was already clear.
Dave Neptune
