Setting up fuge/sump

[natman2]

Ok I have a spare thirty gallon tank that I would like to set up as a fuge or at the very least a sump to expand my capacity. I cant quite get a grip on how these things are plumbed though.

Do I just use a j tube to gravity feed to the thirty gallon from my 75 and then use a [acronym:7e853debbc="power head or Measure of the concentration of hydrogen ions, depending on context"]PH[/acronym:7e853debbc] to return the water to the main tank and if so how do I get the flows evened out.

Also I would think not filling the 30 gallon to capacity would avoid a flood since the siphon at the top of the J tube would break before overflowing the tank but if that siphon for some reason would break wouldn't my main tank flood before the level in the fuge dropped below my return power head.

If your going to suggest some type of overflow box please explain in detail. I have seen them on the shelves but have no experience with them what so ever, i.e what brand to use, what size, how they work etc.

Thanks in advance.