I was just wondering how this works

[sailon1984]

If you have a wet dry filter and the water from the tank comes from a bulkhead on the bottom of the tank, what happens if the power fails, if the return pump isnt running what keeps all the water from the tank from draining and causing an insurance claim and worse kill all your fined friends?

 

[rallysman]

Usually, when it's drilled on the bottom there is a pipe that goes to the upper surface.

 

[Bderick67]

Hopefully you have a stand pipe installed on you overflow.