Originally Posted by copi
I am not trying to be argumentitive, only to understand...
There is nothing better than asking questions if you don't fully understand something.
I tend to agree with you on the U-tube overflow as being more reliable than the CPR style which also relies on a lift pump to work properly. I used a U-tube over flow for close to 20 years and it never failed once. Not saying it can't fail, but IMO
they are very reliable.
The siphon in the U would only be broken if air accumulated there...and that would probably be caused by using a pump thats too weak. What makes a predrilled overflow so much better is there isn't actually a siphon that needs to be kept. Water is pushed down the overflow pipe.
Ziggy, your overflow is definitely different than mine. You say water can enter the overflow from the slots near the middle and bottom? That's pretty scarey. You can't change a bulkhead without draining your tank? If by some chance a bulkhead started to leak, it can drain your entire tank?
My overflow has those slots, but it's only a cover than can be removed. The theory behind that is water will be drawn up behind the cover and into the overflow. Dunno if it actually does that, but I can take out my bulkheads and nothing will drain out of the tank...only the water inside the overflow itself would need to be drained.