If I keep the pump running, it won't lose prime.
If I shutdown the pump for several hour, it loses prime.
There are lots of air in the filter, when I fill the water under the pump lid, all water goes to the filter.
When the pump is running, I see lots bubbles out of return constantly.
My system is relatively simple: skimmer->pump->DE filter->returns
One possible problem I found is the glue-like sealant on top of the pump is not sealing anymore. What is the name of the sealant? Where to find?
Another unrelated question, how to prime efficiently? I use a sump pump and connect the sump pump to skimmer line with a vacuum hose, because the hose doesn't fit on sump pump (garden hose connection), I need both hands to push them together. Then I need another person to turn on the sump pump, then run to turn on the pool pump. With current prime problem, last was a busy weekend.