Reggie, you may have just been promoted to "Head Mechanic"!
![Wink :wink:](./images/smilies/icon_wink.gif)
Sorry, I couldn't pass that one up. This is the bad one-liner we always hear on almost every scuba diving boat we've been on.
But seriously, it sounds like either the pump piston or check valves are not sealing, the joker valve isn't closing properly, or (less likely) your vent line is clogged. Jabsco does make an updated version of the handpump that includes a handle that locks down with a quarter turn to the left. If you don't have this type I would recommend doing the upgrade. Its approximately $70.
http://www.ceshowroom.com/ProductDetail ... oCIsvw_wcBYou might try running a few toilet bowls of hot water from the faucet through the toilet to soften and loosen any deposits before a pump out. Hope this helps.