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"You still have to syphon air out though if you fill it up with a hose, don't you?"
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If you leave too much air in it... yes.
When I built mine (1 1/2 inch pipe) I didn't bother with a syphon air hole, figured I could add one later, it has run from initial prime for 9 months now.
I think they run fine with some air and if running at capacity they are pretty much self purging.
I suspect a poorly fitted syphon tube or a faulty valve would cause more trouble than a little air.
