An elbow connector is used on the sump end of the pvc pipe. This allows water to flow from the tank to the sump . There are (2) 4 way fittings and (5) T fittings shown in the bottom drawing. This gives 10 inlets to suck debris from. The greater number of inlets the larger surface area you can clean of dirt and debris.
The top of fig 2 shows how the bridge looks from the side with the check valve in the center of the bridge and the bottom shows how the bridge is configured to sit on the bottom of the fish tank. This allows for more surface area to draw water and solids into the sump. The larger diameter of pvc tubing used the greater volume of water it will also move into the sump when the pump removes water from the sump tank. Note if you have small fish in the fish tank you will need to screen the inlet to prevent the fish from entering the sump.
Float rafts may also be utilized in the sump tank for growing produce such as lettuce as well.
In order for your fish to survive they require some form oxygenation in the water. There are many quality aeration devices on the market today to meet this need, or you can again utilize 12 volt water or air pumps to force water to move about the tank creating a greater surface area and thereby increasing oxygenation. The more turbulence in the water you can create the greater amount of oxygen gets mixed into the water thereby being able to support a greater density of fish.
If you are using float rafts you do need to protect them from this water flow.
Small simple aquaponics systems
Small systems can be made from just about anything. 2 similar sized tubs can be stacked and fish grown in the bottom tub while produce may be grown from the top tub. Here is a simple configuration to help you. Use your imagination, get creative. This is supposed to be fun, educational and tasty!