My manual bilge pump is mounted on the stbd side of my cockpit - it's a Guzzler 400 with the flush mount kit. The pump is mounted vertically so an up/down motion of the handle does the work. I've never considered it as a problem - I've always been able to pump out with it. However it's always been a bit cranky to prime it - takes a few strokes of the handle to get the water moving. Normal says I.
This winter I'm in the water for the first time. Bilge pump will NOT take a prime - wave that handle up and down until I turn blue, but no water. Started thinking about it and realized that gravity was holding the flapper valves open. Suction is on the top and discharge on the bottom - this is the way it came from the factory! Next warm day I'm flipping that puppy over and redoing the hoses.
Unbelievable..