Hi,
Let me try to explain.
The opening of my inlet was usualy just above waterlevel.
i moved my inlet 2" below the waterlevel and inserted what i think you call a powerhead,a smaller exit to the tube.
This for better waist disposal, and it work nice.
But now when I unplug my pump the water flows back into my sump.
And it will overflow.
I could reduce the amount of substrate in the filter but rather not do that.
Any idea on how to secure the water from flowing back.
If i put less water in the filter, it will pump air if the cotton in my pre-filter clogs!
I use a CV pump on PVC tubing and have got not plugged in electric valves on the tubes,whom i can close manually.
But thats no good in case of power-faillures.
any help is welcome.

i am not sure if your sump filter is a seal lid type. if it is,
you just put the suction and the discharge line to the water tank
and they balanced until no movement at all. fluids will move due to
gravity. any lower side will become the discharge point if you do not
have check valve or equivalent.

yes thats right.. you might wanna go for a closed sump type...

You could also look into getting a check valve that only allows the water flow one way. This will work if your lines are long enough to break and install one.
This is how they work... They have a ball inside of them that when the water flows one way it allows the water to flow but as soon as the water starts to flow backwards the ball is pushed against a stop. Preventing water from flowing the wrong way....Hope this helps

yes i have heard of this.. its good.. but you dont find them to easily

Here is a site that I found that sells what I was talking about....
www.aquariumguys.com/check-valve-2.html

I hope that this helps

woooo good stuff

if the water is flowing back through the new modification you made just drill a small hole into the piping to break the syphon and this might cure the problem your having.

Thats a good idea necro.. I never thought of that

necromancer4 wrote:
That may be the easy thing to do!
Will check out the valve thing .
Thank you!