How does this tank overflow work?

[Miami Reef]

I’m not used to seeing this tank.

can someone explain how it works to filter? I’m used to either a HOB or a sump. This tank doesn’t have a sump (which is good) but how do I work this tank with those holes on the back?

For a coral QT tank.

 

[BostonReefer300]

That looks like an all-in-one tank. The back compartment is essentially a mini sump. Check out any of the nano AIO tanks online from waterbox or innovative marine and you'll get the picture. Also, my guess is that particular tank is going to need a SERIOUS cleaning---and you'll probably want to bleach soak those rocks, rinse thoroughly, and air dry them.

 

[jskoms]

It looks to be an AIO. The return pump would be housed in one of the back chambers.

 

[JumboShrimp]

Same conclusion. Looks like an all-in-one (AIO). A slotted grate will let water flow into the back (looks like 3-4" wide), and you will have a small pump back there to pump water up a return tube and through a round hole in the same wall, to push water back into the tank. Filtration can be as simple as filter floss, etc., ect. Generically, to see some sketches, search "BioCube Instructions" on the web and you'll get the basic idea. Best wishes!