There are many ways to design and build an overflow box. From my experiences, I
have found the following to be the best way to make one and keep it running. To
save time and give you a better chance of being successful, I have included the
lengths for certain tanks that worked for me.

Let’s start with the list of materials needed:

½” Schedule 40 white PVC 90° elbows (slip on type); quantity 5

½” Schedule 40 white PVC “Tee” ½” x ½” x ½”(slip on type), quantity 1

½” PVC end plug(slip on type), quantity 1

1½” PVC end plug(slip on type), quantity 1

10’ length ½” Schedule 40 white PVC pipe, quantity 1

10’ length 1½” Schedule 40 white PVC pipe, quantity 1

Clear vinyl tubing (ID= ¾” ), quantity 1 foot piece  

PVC Glue, qty 1     


Although this is a lot of PVC pipe, it is only sold in 10 foot pieces. Besides you will
have enough to make 3 to 4  more boxes for even less than the original.

          

                                                        








              All the pieces for Overflow Box cut & laid out

Tools Required:

Hacksaw

Utility knife

Tape measure

Marker pen

Ok, first off we need to figure out how tall to make our overflow box. We measure
the inside of the tank we are building it for from the glass bottom to the very top of
the plastic frame with the tape measure. Next measure the height of the tank to the
desired water level you want. Remember to allow at least ½” over top of the overflow
box, for water flow (you can make the overflow box shorter, if you don’t want to
water levels to get this close). The height of the water we want in the tank will
determine the actual length of the overflow box (1½” PVC). As a general guide I use
the bottom side of the tank tops plastic frame as a desired level of my tank water.
This still gives the room needed for the waters hydrostatic head to start the siphon
of the overflow before it reaches the underside of the tank cover. To help simplify the
measurements I have included the lengths I use for various tank sizes.




                    1½” PVC with plug cap (the actual OFB)

- 20 gallon Tall tank,  1 ½” PVC length = 15 ¾”

- 29 gallon tank, 1 ½” PVC length = 16 ¼”   
      
- 55 gallon tank, 1 ½” PVC length = 18 ¼”                                                

We measure out the length of  1½” PVC we need for the overflow box and mark it.
Cut the PVC with the hacksaw, trying to keep the cut as square as possible but don’t
worry if the cut ends up a little crooked. As you cut the PVC you will notice a burr
will form on the inside and outside walls of the PVC. We scrape off this burr with the
utility knife after we finish the cut with the hacksaw. Make sure that all the burrs
and cuttings are cleaned out of the inside of the PVC. Banging the pipe on the floor
or blowing them out usually works.

Now we have to figure out how long a piece of ½” PVC we will need to get the loop
up over the top of the plastic tank frame. Remember when we measured the inside
from the glass bottom to the top of the plastic frame, we can use this measurement
now. We subtract ½” off this measurement and this is the length we require for the
first piece of ½” PVC.  Again I have included the lengths I use for various tank sizes
to save you some calculations.

- 10 gallon tank,   ½” PVC length =  11½”

- 20 gallon Tall tank, ½” PVC length = 15 ¾”

- 29 gallon tank, ½” PVC length = 17 ½"

- 55 gallon tank, ½” PVC length = 17 ¾”

Ok hope you are still with me? I measure from one end of this piece 1¾” and make a
mark. This will be where the top of the 1 ½” PVC overflow box will be glued to this
piece of ½” PVC. We need to cut a second piece of ½” PVC to the same length as the
last piece. This will be for the outside of tank loop and will hold the overflow box
tight to the side of the tank. Measure the PVC to the required length, mark it, and
cut it with the hacksaw as before. Remove and clean out the burrs and cuttings from
each end after the pipe is cut.

The riser is the last piece of the overflow before it goes through the Air Stack “T”
and off to the drain. This piece should be less than ½ the length of the overflow box
(1½” PVC). Again I have included the lengths I use for various tank sizes for your
convenience.







- 10 gallon tank,   ½” PVC length =  5¼”

- 20 gallon Tall tank,  ½” PVC length = 7 ¾”

- 29 gallon tank,  ½” PVC length = 8”

- 55 gallon tank,  ½” PVC length = 9”

The last pieces we need to measure and cut allow us to attach two of the 90º elbows
together to form a 180º “U”, as well as the two pieces on each end of the “T”. There
are actually two 180º “U” s required for this box design. To keep things simple I use
the same 1½” length of  ½” PVC for all four of these pieces. Remember that all burrs
and cuttings need to removed and cleaned out of the PVC before we glue anything
together.







Putting It All Together

First piece to glue is the ½” piece of  PVC with the mark on the one end to the inside
of the 1½”(Overflow Box) piece of PVC. Generously add PVC glue to outside of the
½” piece of PVC from the mark, length wise down to the bottom(the short end to the
mark is to be considered the top). It is not necessary to glue the entire outside of the
½” piece, only where the ½” piece will make contact with the 1½” piece PVC.







While waiting for the overflow box to set up(give it 12 hours to set properly), glue
two 90º elbows together using a 1½” length piece of  ½” PVC to form the 180º U. The
glue sets up quick(15 to 20 seconds), so make sure they line up to form a perfect “U”
before the glue sets.  We need to construct two of these “U” s for this project.








Next day start off by gluing on the 1½” PVC plug cap to the bottom of the overflow
box (1½” PVC pipe).













Glue Riser piece (1/2” PVC tubing) into the bottom side of the elbow.









Now add the bottom “U” to the bottom side of the long ½"
PVC tubing again dry fitting it first then marking it with
alignment marks on the joint. Position this connection so
that it points in the general direction of drain then glue it.
The last piece to connect should be the bottom of the “U” to
the Riser piece, again use alignment marks to make sure it
is pointing in the right direction before gluing. Your
overflow box should look similar to the one pictured here.
The last thing we do is attach a piece of vinyl tubing from
the “T” to the drain pipe.


Priming the Siphon of the Overflow Box

Now that we have the box built the last thing we need to do is prime or remove all
the air from the siphon for the overflow to work. We do this by removing vinyl
tubing and slipping a ½” PVC plug on the end. Don’t push it on too tight as you will
need to remove it quick once we have all the air removed from the overflow siphon. I
attach a water hose from the sink to the top opening of the “T” . I made an adaptor
that has a garden hose union on one end and a ½” PVC tubing on the other.

This way I can slip it into the top of the “T” and were ready to turn on the water.
Make sure the overflow box is in the sink when you do this as the water will flow
out pretty fast. As the water flows you will see air bubbles come out the overflow
box, just keep running the water until no more bubble of air come out then shut off
the water. Remove the supply hose and the end cap as quickly as possible. If you don’
t remove both, the siphon will suck air back up into the top of the loop and you will
have to re prime the siphon again. When you get it all done keep the overflow box
standing up to prevent it from draining. Add the clear vinyl tubing back onto the T
and slide the box into the tank. Make sure vinyl tubing is in the drain or you will
end up with water everywhere as soon as the box top drops below the water level. I
attached a cut away view of the overflow box so you can visualize the explanation.
Do It Yourself Over Flow Box
Photo Caption For Above
You can see the old style OFB in
the back here.
New Jersey FishyBiz                            " When Quality Counts and Service Matters "
Riser Piece
1/2" PVC to get up and over the Tank
Pieces Forming the 180º U
180º U
Photo Caption For Above
This was one of our early designs
but shows the OFB ready to go in a
tank. You can see the 1 inch clear
plastic vinyl tubing from the OFB to
the drain pipe in the back. We
replaced the 1/2" OFB with the
current  1 1/2" OFB and use less
pieces to build it.
Spread glue the length of the 1/2"
piece. Remember to leave 1 3/4" will
need to have this to glue the 180 U
onto later.
Glue the two 90 elbows together to
form the 180 U, remember to line the
elbows so that the U does not twist at
all. You will need to do this for both U's.
Glue the “T” to the fifth 90º elbow,
make sure the elbow is facing
180º from the open part of the “T”
as it is in the picture.
Glue the last
long piece
of  ½” PVC
tubing into
one of the
180º “U” s.
them first over the top of the tank where you want
the overflow box positioned. This way you can set
how tight the box fits to the tank. Then add
alignment and make marks on the PVC joint, pull it
off the tank and glue with the marks aligned.