Those leaky lower-hose drain petcocks!

[Fred K-OR]

Don't you also need to make sure the thing that turns is "seated" in the body of the valve? In otherwords the spring on it may not hold the turn cock tight enough to get a good seal. May help to lightly tap the cock in on the latch end of this cock. (My terms or out in left field but you may get the idea of what I am trying to say)