Is This How External Filters Work, Total Newb

[Sweeden]

 

[TwoTankAmin]

External can mean a canister filter or a hang-on filter? That as opposed to an in-the-tank filter or a sump system.
 
But yes you your drawning as to how they work, the principle is the same for all externals including sumps. The flltration takes place outside the confines of the tank.