question about durso drain

[mister crabs]

ok so i just setup my first plumbed tank. I drilled a glass oceanic 40 stretch hex in the back. I setup an external durso drain where the elbow is on the inside of the bulkhead inside the overflow and the rest of the drain setup including the tee and the cap and such is outside the tank. Its a 1" drain (pvc) and a 1" return. My sump is a 10 gallon with baffles and my return pump is pushing around 450-500 gph.
my problem is that the water level in the overflow builds up ahd then drops all at once. Its got a distinct rythm to it. its what i have heard is called a "flushing" effect. my question is how do i fix it?
I have tried lowering and raising the output of the drain anywhere from 4-5" under water to above the water completely. doesnt help. I tried throttling back the output of the return pump with a ball valve and it doesnt seem to affect it either.
I also dont have a skimmer running yet (doing WC weekly) since i dont have any livestock in there yet just rock and sand. But i do seem to be getting alot of microbubbles which i understand corals dont like. how can i get rid of them? thanks in advance guys for your help!

 

[silverwolf72]

Do you have a hole at the top of your tee? Sounds like your creating a vacuum.

 

[DrBegalke]

also, is the drain pipe continuously pointed or sloping down? any upbends, and especially any loops in a hose, will do this.

 

[mister crabs]

drain goes straight down then hits a 45 and slopes into sump. yes there is a hole. and now it makes a slurping sound to boot. aarrrghhhh......stupid sumps and plumbing....bah

 

[Entropy]

Sounds like your hole is too small. Try making it bigger.