I did the hole idea and seem to be working great. But now i have gurgling in the overflow to were it connects with my return line

Aren't there benefits to returning the water to the bottom of the tank are removing from the top.  I would think it would give you better water cycling.  Is that not as important?

If you have powerheads rolling water on top, or lets say you do that in your sump.  Can an arguement be made that returning water to the bottom and overflowing off the top is better then returning water to the top?

jfinch wrote: Check valves are a fine addition to the system (get the ones with a swing check rather then springs, imo) but I would never put all my trust in one.

I agree with Jon.  I would add a check valve (swing valves are much better then spring valves, as Jon mentioned), but would also drill the holes in the returns.

I have seen one to many check valves fail.

I would go with the drill idea.  Just remember that where ever you drill the hole there will be a water spout so it needs to point into the tank.

Here is one of my nifty diagrams.  You can drill in either of these spots to create the siphon break.  Just remember that when your pump is on, water will be shooting out of the hole.  (I hope that someday my diagrams will be famous.)

Check valves are a fine addition to the system (get the ones with a swing check rather then springs, imo) but I would never put all my trust in one.

I put a check valve in right after the pump, that way I don't even have the water from the lines coming back in.  My sump is fairly small so I do not have much difference between my "min" and "MAX" levels on it!  Maybe some day I'll get a bigger sump for that tank.

The only issue (I believe) you will hear is that a check valve causes a loss of pressure/volume.  You have to make the decision as to what will work the best for you.

Good luck.