Another option is to forego the ball valve altogether. I just have the tubing come directly out of the cooler and I tuck the end of the tubing up into the handle on the cooler. When I want to drain, all I have to do is to lower the tubing into the kettle. To stop, lift the hose up again. Easy peasy.
this is what I do too. never (knock on wood) had a problem yet. I don't see it as any more likely to cause a problem than forgetting to close the ball valve.
Would not recommend this method.
I had this system for one brew day before the hose came loose from the clamp, sprayed 154F wort on my jeans and into my shoes. After attempting to secure the hose above the liquid level again, I had to kick off my shoes and rip off my pants due to the sopping wet hot mess I was wearing at the time. The kitchen was a sticky mess, my shoes and pants were a sticky mess, and the rest of the brew day was barely salvageable.
Safety first guys! Get the gate valve that Denny linked as a preventative measure at the very least.