How do I keep my well pump connections from leaking?
From my answer before:


  When you connect this pipe to the fittings, you'll need to heat it up (I prefer MEP gas but propane works as well) just enough so it can go on (you still need to apply a bit of force). If you heat it too much to the point it stretches, you'll weaken the pipe and probably cause a leak - if you do this, cut the end off and start over. Use two stainless steel gear clamps to ensure a reliable connection (you can usually get away with one -- but in an outside location like a well, an extra couple gear clamps is probably cheaper than the pain of having to do this repair again).


If it's leaking, then:


You heated it up too much. 
There is something wrong with the barbed connector (eg, a cut through the barbs). Brass male adapters are usually better than PVC. I personally don't like nylon, nylon fittings seem to wear out really quickly after attaching/detaching just a couple times.