What’s this do

[BlueLineAquaticsSC]

I bought one of this cheap airline connection kits off Amazon and it had these pieces with it. Can anyone tell me what they are/do.

[Tihshho]

It's a check valve that prevents water from back siphoning to your pump if/when it loses power. Sometimes the cheap ones don't work, but you can test it by blowing through it, should only allow air to pass one way.

[Garren]

They are a check valve. It will prevent water back flowing through an airline if the pump shuts off.

[Odd Duck]

On 9/6/2021 at 8:35 PM, BlueLineAquaticsSC said:

I bought one of this cheap airline connection kits off Amazon and it had these pieces with it. Can anyone tell me what they are/do.

That’s a check valve for your airline.  If your electricity goes off, or your air pump stops working, the airline can become a siphon and drain your tank.  That needs to be installed in the airline with the pointy end aimed at the tank and away from the pump.  If you’re ever in doubt just blow in each end.  You should be able to blow easily in the direction of airflow and should not be able to blow against the direction of flow.  I usually install it down at the air pump end just so it’s more hidden in the stand and less stuff that might be visible behind the tank.