All these auto-top offs...

[Majestic_Aquariums]

Hmmm. That makes sense when you think about it. For the purpose I need, I would have it plumbed into the sump directly, right off the water pressure of the house though. (for freshwater) The one that I have is about 2 1/2" in diameter, and 10" tall, so size isn't a prob.
For the marine however, you couldn't do that, unless you want to be mixing salt in the sump!
Thanks for the help-and not flaming me for such an idea!!