What would be best way to filter 4 soon to be 5 ten gallon tanks

[rcombs]

I built a stand, and now have my tanks set up. They are running with heaters and an airline to each tank. I have no filtration set up as of yet. I do 2 water changes a week. I like to run sponge filters. Would it be best to just convert my airline in each tank to a sponge filter, or should I add a sump. If i add a sump, Would it be best to drill each tank or do the hang on back siphon out of PVC. Also, I don't want the fish smell of a tank to fill the room. Any suggestinos for that?

[danielratti]

Sponges would be cheapest and easy.