Question!

[Delphinus]

You can pretty much fill it anywhere you like. The closer to the top, the greater the risk of overflow, but there's no reason structurally, to stop a few inches below the trim. In fact, when I put in overflows on my tanks I try to make the water level just above the bottom of the trim line because I think it looks better than seeing the waterline. Plus you get salt creep and so on above the waterline, which is unsightly.

Hope this helps..