I like to try new things and concepts and folks this is an awesome awesome idea for us NPT ppl. I have two tanks at home 10 and 20 and have these small community fishes in there. I always wanted to connect the two tanks together so that the fishes can swim between the two. I first thought maybe drilling holes and connecting them with a small bridge. That idea was shot down as it is too much trouble. Then after some search, I found the concept of siphoning and came across the "fish highway" web site and it inspired this water bridge concept. Basically it is a upside down "U' shaped siphon that allows the small fishes to go through. I found that they sell 1.25" and 1.5" U-Tube siphon on the web perfect for allowing small fishes to swim through from one tank to the other. To create circulation, a water pump can pump water from one tank to the other and the water flows back to the other tank through the u-tube which create a cycle and current all at once. That way you only need one pump for two tanks. Since NPT tanks don't need filtering...just water movements, this would be an ideal and awesome concept. Plus with 1.5" diameter tubes, it will fit the tank without modding the cover. Unfortunately my tanks are at different height level and this idea only works when the water level of the two tank is parallel or close to it. I have read that fishes don't travel back and forth too much. But that's inconclusive since only one person mentioned that and there are very limited amount people who knows about this. Imagine you have two 55 gallon tanks. Connecting them with this "water bridge" makes the tanks seem like a 110 gallon tank with the option to turn it back to two tanks in matters of seconds. Get to it people and tell me how it goes. I am thinking of raising my 10g to the height of 20g just to try this out but thought I give you guys the info ahead of time. I don't know any easy way of raising the tank right now as one sits on a small table and other on a tank stand.