What have you used to filter a 300 gallon stock tank while indoors?

List them off Ive become stumped with how to filter on the inside of a house.

Ok, I looked at old posts, and iam thinking of converting a 30gallon plastic storage container that would rest on top of milk crates, providing a cave and filter stand, and I would use 600+ gph pump to pump water to it, I would fill it with cinder sand and cinder rock. this i hope would provide mechanical filtration and enough surface area for bacteria to colonize also. water will pump up through it and pour out into pond or go through pipe into pond.

Hows this sound?

I am making sure my idea's seem sound and would like other sound ideas for filtering the 300 stock tank, I wont use bioballs due to cinder rock being cheaper and fullfiling the same job, unless yah know of a source for sponges or bioballs dirt cheap or free.