Operating a Store Pump System?

[esn]

So to get me to come up for Thanksgiving with my axolotls, my grandmother went out and picked up a used tank from a pet store. It came with some sort of water-pump/filtration type contraption (that used to be green before I scrubbed it) for use over their gravel with airstones. I have no idea how it works. Also, as I use sand, I have no idea what it will do.

The pictures are the pieces of the contraption without the airline tubing and air pump. Apparently it attaches and does... something? I was told that the plastic grating goes at the bottom of the tank. I can't figure out if it's to be over or under the substrate. If anyone here can't figure it out, are there any ideas of how to do this without the grating? It's pretty ugly. I normally just have airstones in my tank, but I'm interesting in how this is supposed to help change water and filter.

For now they're just sitting in their dark tank and doing just dandy without it. But I'm going to be taking the tank home with me since it's larger, and I really would like to know how to work this.

 

[Chirple]

It sounds like an under-gravel filter. https://secure.wikimedia.org/wikipedia/en/wiki/Filter_(aquarium)#Undergravel_filters

I don't know if it would work as an under-river-rock filter (since it's bad for axolotl's to be kept with actual gravel).

I would probably just use something else, but maybe there's a way to work with it.

 

[esn]

Thanks! I've taken out the grate, but am otherwise using it as an aerating system. I usually just shift around my sand some to aerate it, but my axies love the increase in airstones.