Check valve

[pip walters]

Oh, ok. Then you don't need the valve

 

[dilger]

I always buy 5 at a time because I find that they are not all the same some are more free flowing then others and if UR unlucky enough u'll get a dud
I run one regardless of pump location
Might help to depending on the air stone size whether it's a 20cm long or 80cm long one etc you might need a bigger pump to get the air bubble result you want/need

 

[cfosgate]

With the pump located above the tank you can just remove the check valve.