Weird plumbing question

[DanConnor]

OK, try to visualize this: I have a sump drilled in the side; on the inside of the bulkhead the pipe elbows 90 degrees and extends 4 inches down. On the outside it goes to a floor drain with no syphon. When I open the outside valve, the water level should fall not to the bottom of the 4 inch pipe, but to the bottom of the hole in the tank, correct?

If I placed an S pipe outside the tank and before the ball valve, the pipe would stay filled with water, and the level when opened would fall to... the bottom of the 4 inch pipe?

I'm having trouble grokking this.

The reason I am asking is I have drilled my sump at the desired water level so I can open it to a drain. Above the sump is a 50 gallon tank that will be filled with salt water and will flow to the sump near the return pump. So to make a 50 gallon water change, all I have to do is open 2 valves.

However, I'm now thinking that when the return is shut off, the bits of the 200 display and the 2x4 foot frag tank and the contents of the pipe will be too much for the top 1/3 of the 75 sump to handle. So I'm trying to see if I can have a lower sump water level and still find a way to do my sweet no-pump water change system...

 

[DanConnor]

The sump etc is in the basement, if that wasn't apparent

 

[AllSignsPointToFish]

If I understand correctly, you are still creating a siphon. A picture would be really helpful. If you want the water level drop to stop at the elbow, drill a hole in the top of the interior elbow to break the siphon.

 

[DanConnor]

The purpose of the elbow is to try to lower the standard water level in the sump, so my goal is to not break the siphon. There will be a valve outside closing the drain when not making water changes.

 

[AllSignsPointToFish]

How long is the outside pipe to the drain after the valve?

 

[DanConnor]

about 5 feet sloping slowly to a floor drain. The tank is on the floor too.

 

[DanConnor]

On second thought I think it would drain to the bottom of the pipe regardless

 

[AllSignsPointToFish]

If siphoning, then yes you are correct. It's really no different than the 180 bend in an overflow box draining all the way down to the end of the bend (unless you've drilled the elbow to break the siphon).

 

[DanConnor]

Thanks