For multiple tanks you want to use a sump-siphon system.
The siphon is actually easy to build. Since you're not doing a skimmer overflow siphon all you need is some fittings and vinyl tubing.
1. For getting over the top of the tank edge you want a pair of fittings to make a "U" aimed down.
2. The siphon side on the back will also need another "U" aimed up,
3. Above the sump side of this "U" at the water line you want a "T" fitting that continues up AND goes to the side. Where this T goes to the side will determine the waterline point. Do not seal the hose/pipe that is going further up, let it stick up about an inch above the top of the tank and leave it open.
4. On the sump side of this "T" you want a 90° fitting that leads downward through a hose/pipe that will go to the "sumping sewer".
5. The "sumping sewer" is a pipe that collects the water and leads it to the actual sump.
6. Fun in the sump... Keep in mind that the sump need only be far enough below the water level of the tanks to allow the water to collect and go into filtration. The "sumping sewer" can be enough sump for a barracks arrangement, then the lower end has the intake to a pump on it, which can force water through a canister filter left unplugged with its impeller removed. The issue is that the pump in the canister filter will not be enough to return the water to the tank without risking a burn-out. Canisters rely on neutral static pressure between intake and output.
Your other option with the sump is a classic stack-box sump which lets the water directly pour onto filter media then dribble through each layer of the stack box. A 5 gallon aquarium is enough sump for twenty gallons with a heavy flow.
Its all rather complex and central and exposes all your fish to each other's diseases. In a large array with UV sterilizers and automated water control systems it makes sense.
But in a barracks arrangement for home, just use Hydro Sponge #0's primed with Hagen Cycle, Mardel's biological stuff or TLC's tank bacteria culture (last is best) in each individual tanklet.
Air pumps to run them are about $6.00 each at Walmart. So $12.00 per barrack tanklet for great aeration, filtration and happy healthy safe fish.
(TLC Optimizer for Freshwater Aquariums, Aquatic BioControl, Westlake OH.)
I've used ONLY the TLC product since Marineland stopped shipping NitroSpira pouches.
Last edited by Thunderloon; 11-14-2011 at 12:25 PM.