I changed the water pump, and now the drain valve will not stop dripping. It's about 1 drop every 3 seconds. How does the dang thing come out so I can replace (I'm guessing here) the o-ring? It's a plastic petcock, kinda like a water faucet. The valve turns out about 1/4 to 1/2 turn, then catches some coarse threads to unscrew until it hits a stop. Anyone know how to get it out?