The one drawback about how I do it is if I drill the hole in the wrong spot then I'm stuck with a hole I either have to live with or patch, and either way sucks. The hole needs to be about 1.5" (maybe more, I can't remember for sure offhand) above where you want your waterline. So a slotted attachment point instead of a hole allows you to position the valve where you want it, as long as you can still attach it solidly (ie., any wiggling would be "bad"). And then if you want more water or less water in your sump you can adjust the valve to a new position and retighten, rather than drill a new hole.
But the slot then has to be IN the sump of course, and not the tank wall.
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-- Tony
My next hobby will be flooding my basement while repeatedly banging my head against a brick wall and tearing up $100 bills. Whee!
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