You basically put two ends of the bridge into two full aquariums, push in a tube and suck out the air from the bridge. As air is sucked out, it is replaced by water. The problem is, dissolved gasses in the water will constantly accumulate (gas out) inside the bridge, so you would need to suck out air on regular intervals. Best way is to have a release valve on the highest part of the bridge so that you can suck out the air out when needed.