Question on return line syphon

[krabbo008]

So I picked up this 300 a few months ago. My question is, it is drilled on the side of the weir for returns. The holes are 6" from the top of the tank. I want to prevent back syphon as much as possible to limit how much water drains into the sump when the pumps shut off. the sump(s) I plan to use are small. If I capped the top of the T and drilled a few small holes at the top would that stop the syphon? How big/many holes would be recommended?

 

[wednesday13]

One 1/16"-1/8" hole would break the siphon as long as its not clogged... dont want to big a hole then ur just shooting fresh water back to the sump...
You could also just install a good check valve in the line to prevent back flow/siphon. This would allow the least amt. of water if any to pull back through during power out or pumps off.

 

[takagari]

Never trusted check valves, little bit of debri and it doesn't seal.
A few small holes would be best, just enough to suck in air.

 

[Dixon81]

Yea, small hole in pbvc just above the water line will break the siphon.

 

[DN328]

Break siphon hole is good. Where you plan to drill the whole seems to be same height as locline return too. I have mine near the surface for agitation and will drain to where my sump can accommodate.