Issue with trickle filter overflow tube.

[puffers4puffers]

About 20 years ago I was experimenting with a CPR overflow after picking one up used.
It could never hold siphon without help.
View attachment 1533380
As you can see above, and below I attached the venturi port of the powerhead with airline tube, to a drilled port in the overflow box.
View attachment 1533381
As long as the powerhead was running and the venturi would suck air, the siphon in the overflow held.
View attachment 1533382

Yes, it is the issue with such an overflow unit.
Definitely NOT a recommended product

 

[krichardson]

About 20 years ago I was experimenting with a CPR overflow after picking one up used.
It could never hold siphon without help.
View attachment 1533380
As you can see above, and below I attached the venturi port of the powerhead with airline tube, to a drilled port in the overflow box.
View attachment 1533381
As long as the powerhead was running and the venturi would suck air, the siphon in the overflow held.
View attachment 1533382

I also have that type of box on my other tank and it is not without its own issues as well!