head doesnt flush
Two or three times a year my intake thru hull gets clogged with biomass. I take my hose, from my dock, into the boat. Then I connect a special purpose , mickey mouse, homemade, home depot connector to the intake thru hull and blast it back out from the inside. I also lean over the side of the dock and scrape the outside of the thru hull with something soft, like a paint stirrer, until I feel a free flow of water from the inside out. Usually does the trick.
As an aside my ant siphon is between the intake and the head and prevents a siphon from starting that would overflow the lavac and not stop until something made it stop.