I find I need to run around in a lake a bit till the thermostats in the main and kicker open up if I want a really good flush.

Up until a few years ago Wooldridge did not put zincs on all the pumps they mounted. They do now, but without a zinc in salt a pump will start corroding fast.

One other thing to note, is that without good zincs and using downriggers the ground voltages will be screwed up, I know commercial skippers who will swear themselves blue in the face that a boat with more zincs will catch more fish just due to the voltage difference.. I still think it sounds fishy