I have made a few overflows in my time, but it always seems like the parts list for diy overflows can be a little tricky. They often require bulkheads or other hard to find parts. This overflow is easy to make and all of the parts will be available at your local hardware store. The total price for the parts for this build is less than $15.00.
(7 each) - 3/4" PVC elbow fittings
(1 each) - 3/4" PVC three way tee fitting
(4 foot) - 3/4" PVC pipe
(1 each) - 3/4"x3/4" PVC slip barb adapter
(1 each) - 1/8"x1/8" Nylon threaded barb adapter
(1 each) - powerhead OR (1 each) aquarium airline shot off valve
(1 can) PVC cement
They say a picture is worth a thousand words, so I guess we have three thousand words here. :)
Here is the view of the finished pvc overflow from the right side of the tank.
Here is the view of the finished pvc overflow from the rear of the tank.
Here is the view of the finished pvc overflow from the left side of the tank.
To make it a little easier to refer to specific parts of the overflow, I color coded them in the diagrams. The blue section is the intake section of the pvc overflow. The yellow section is considered the resevoir area. For a typical diy overflow, this is usually some kind of open container like a specimen container or a water pitcher. We are recreating the same effect in a much simpler way by using pvc pipe. The green section is where the water overflows into and drains into the sump. The red section is the only section of the pvc overflow that does not have water flowing through it. Instead, it server a few important purposes:
1 - It acts as a siphon break.
2 - It serves as a hanger to hang the pvc overflow on the back of the fish tank.
3 - Because the elbow on the inside of the tank is not glued, it can be turned up to allow the filling of the yellow/blue chamber.
Step 1 - Cut the PVC pipe: Cut the PVC pipe into the appropriate lengths. You can customize the size of your overflow, but please make sure that the center of the yellow tee join is about even with the desired water level in the tank. A good average size for the long blue pipe and long green pipe is about 14 inches. You want to cut the top red and blue pieces to the shortest length possible to make the siphon hang on the tank as tightly as possible.
Step 2 - Dry fit the pieces: Once all of the pipes are cut to the appropriate length, assemble the overflow to make sure it hangs evenly on the tank. Also make sure that the yellow tee is even with the desired water level in the tank. This is a critical step and can cause serious problems such as overflow or low tank water level if you don't have it set right.
Step 3 - Glue the pieces: After you are certain that the overflow is level and the yellow tee is at the desired water level then you can go ahead and glue the pieces together. Do not glue the red elbow that will be inside the tank because this needs to be turned up to fill the center chamber of the overflow.
Step 4 - Install the 1/8" barb fitting: Drill a 1/8" hole in the top of the blue PVC pipe at the top of the overflow. Tap it out with a 1/8" tap to thread it. Screw in the 1/8" barb fitting. If you do not have a tap, you can drill the hole out a little extra and super glue the 1/8" barb fitting in place. Just make sure that it is not leaking air.
Step 1 - Hang the overflow on the back of your aquarium.
Step 2 - Attach a 3/4" hose to the 3/4" barb fitting at the bottom of the green pipe.
Step 3 - Attach the aquarium airline tubing to the 1/8" barb fitting on the top of the overflow.
Step 4 - Turn the red elbow so it faces up. Trickle water into the elbow to fill the middle chamber.
Step 5 - Once the middle chamber is filled, turn the red elbow back down so it faces the water inside the tank.
Step 6 (If you have a powerhead) - Attach the aquarium air hose to the inlet of the powerhead to create a vaccuum. This vaccuum will automatically prime the overflow and it will begin operating.
Step 6 (If you don't have a powerhead) - Attach the aquarium air hose to a on/off valve. Open the valve up and suck on the end of the valve until you see water in the air line hose. When you see water in the air line hose that means the overflow is fully primed and should be operating. While maintaining suction on the hose, close the valve.
Step 7 - Your overflow should be operating. Check for leaks and make sure everything is operating as planned.
An internal skimmer basket can be added inside the tank to keep fish from being sucked into the pipe.
You could cap the end of the blue pipe in the tank and drill 1/4" holes in the blue pipe below the waterline to get the same effect as a skimmer.
This design should be fully scalable. Just use larger diameter pipe to increase water flow. I have not measured the gph of this overflow but it seems to have no problem keeping up with my 200 gph pump.