Re: Manual water pump priming sucks so much ....
You have a leak, but it's an air leak.
Air is leaking into the system, probably at the diaphram inside the pump. Hence, you lose prime, but no water leaks out of the system.
Here's what I did: Dismantle the pump and soak the diaphram in a light coating of veg oil. It's safe for humans, and often causes the rubber to swell and moisten, and retain its prime.
S/V Old Shoes
1973 Pearson 30 #255