Originally Posted by firstbase
For the record, if anyone knows where I can get two of the rubber cones for the SVS series, 1000 and 750, I would REALLY appreciate you letting me know.
One place where the air can come in if the rubber cone is shot is on the handle side. Other side is a threaded T handle. Hard to imagine air drawn in there, and you would think the lower seacock would be dripping wet if it had a leak due to worn rubber cone. And it ought to at least be weeping in some sea water visibly if the lower seacock is bad.
Are you tightening up the T handle to seal the rubber cone tight to the housing?
Take some toilet bowl wax ring, dry the bronze seacock best you can, smear the wax all over the side handle cover, bolts, T handle threads, any where you think it might leak and see if it at least slows down the air coming in. That wax should stop any air being drawn in from somewhere.
I wonder if your rubber hose-clamp-water pump has a defect.