Can take longer than 20 secs to fill the power head & start coming out of the teltale, I'd give it a minute. When you're on the hose, the water is under pressure & being forced into the leg. In the tub, the impeller has to prime itself, as already mentioned, if you can get the leg immersed until the water pump housing is below the water level, this will help. The pump housing is at the top of the gearbox, just below the split.
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5