First fitting is a 1 inch threaded male adapter which screws into the threaded bulkhead. Be sure to use teflon tape on the threads, you want this to be a water tight seal.

Next, I convert the 1 inch pipe to a 1 ¼ inch pipe using a reducer bushing. (There is a small section of 1 inch PVC pipe linking these two parts, use plumbers tape on both ends). The reducer bushing is then inserted into a coupling.

Then the standpipe is inserted. The PVC pipe is Schedule 26 type commonly called PVC thin-wall pipe. It is thinner, lighter and drains better than schedule 40 pipe. I used PVC cement for this connection to keep it water tight.

At the top of the standpipe is a 1¼ Tee fitting. This is attached to the standpipe with plumbers tape only. I wrapped it around 3 times to get a good tight seal. By not using PVC cement, you can later cut the PVC pipe if you find the water level is to high.

A special elbow connector called a "street-ell" is then inserted and pointed directly downwards. This is the water intake, it will always be submerged. Since it is submerged, it can not suck in air.

Note: A street-ell allows the ell to be inserted directly into the Tee fitting without requiring a separate small PVC pipe length to connect the elbow and tee together. A standard PVC Elbow can be used but may not be as compact as the street-ell. To fit into small AGA style overflows, just trim the street ell connector down. Only about ¼ inch is needed for a gluing surface.

Use PVC cement to connect the Street-Ell to the Tee. On the top part of the Tee fitting, insert a small section of PVC pipe which should be glued in. Finally an End-Cap fitting to top the unit.

The End-Cap is held on with teflon tape. A very small, as small as I could make it (thickness of a toothpick), hole is drilled in the top of the End-Cap fitting. This allows some air to enter into the standpipe. This size air hole worked well for my setup, you will likely need to tinker with it. I would suggest starting with a 1/16 inch drill bit for the air hole in the End-Cap. If you find the water level in the chamber fluctuates quickly then the standpipe needs to suck in more air. Try a 5/64 inch drill bit to make the hole slightly larger -- increasing the size if need be. Do not be surprised if you need to go as large as ¼ inch with the hole size. The lower the flow the larger the hole size needed.

The hole on the top of the standpipe (in the End-Cap) is very important. Without the hole, a full siphon will be created and water will be sucked out of the overflow chamber to fast. The water level will drop below the intake and you will get a terrible air sucking noise. If you drill a hole and the water level still drops to far (making a sucking noise) then the hole is to small. Just make it slightly larger (see above) and the water level will raise. If you make the hole to large then the water level will be to high. (It should not overflow the tank as it will not get that high, but keep an eye on it). If the water level is to high this can be fixed easily. Seal the hole with aquarium safe silicone and use a toothpick to make a small hole in the silicone. If this turns out to be to small, remove some silicone with a smaller drill-bit or some other tiny sharp object. No silicone handy? You can try some old well chewed bubble gum to reduce the air hole size for testing If you really mess up, then get a new End-Cap (they are cheap).

Ideally the water level in the overflow chamber will be about 1.5 to 2 inches lower than the display water level. This provides for gas exchange and prevents a slime film from building up on the water surface of the overflow chamber. If you designed it correctly, the water level in the overflow chamber will be a few inches lower than the rest of the tank, and the water level will be at about the middle of the Street-Ell fitting as pictured in the introduction page. If the water level is slightly higher, no big deal. As long as the overall water level in the chamber is a few inches lower than the rest of the tank its good enough.

Standpipe Drawing

10 - 1¼ PVC end-cap with vent hole.

9 - Connector made of 1¼ PVC. Glue to Tee, teflon taped top for snug fit with End-Cap.

8 - 1¼ PVC Street-Ell. Trim the connector for a compact design to help fit into smaller overflow chambers. Glued into Tee fitting. This is the water intake for the standpipe. Water level would be expected to be around the middle of this fitting.

7 - 1¼ PVC Tee. Do not glue this onto the standpipe. Use teflon tape on the standpipe for a snug fit. This allows it to be removed for height adjustment or maintenance.

6 - 1¼ PVC Pipe. Sized long enough to get the end-cap just about equal to the rim of the display tank.

5 - 1¼ PVC Coupling. The stand pipe and reducer bushing are glued to this part.

4 - 1¼ to 1 inch reducer bushing.

3 - Connector made of 1 inch PVC. This should be glued into the reducer bushing. If you have a slip bulkhead, this inserts directly into the bulkhead -- use teflon tape for snug fit.

2 - OPTIONAL: 1 Inch PVC Male adapter - only needed on threaded bulkheads. You may want to attach to connector with teflon tape to allow for a quick yank removal from bulkhead. Use teflon tape on threads before inserting into bulkhead.

1 - Bulkhead. The opening at the bottom of your overflow chamber to allow water to drain out to the sump. This drawing shows a threaded bulkhead.

Frequently Asked Questions:

Flushing Effect: A commonly reported problem when first installing standpipes is what I call a flushing effect. The water level in the chamber bounces up and down at a slow steady cyclic pattern. This is different than the issue above where the water level stays to low. This issues typically is not caused by the size of the air-hole in the end cap. The flushing effect is almost always caused by back pressure in the drain line. Typically the back pressure has two main causes:

1. Drain pipes in the sump being submerged below the water surface to far. Ideally you just want the drain pipes submerged about an inch or two. Just enough to reduce the splashing noise in the sump.
2. Any loops or dips in the drain lines if using flexible tubing. If using hard PVC pipe for the drain lines make sure they always have a slope to them, don't make them perfectly horizontal or perfectly vertical.

The flushing effect works like this: Back pressure in the standpipe prevents air in the pipe from exiting the drain line. Instead of exiting the drain line, the air bubbles try to rise in the pipe slowing the rate at which the pipes drain. The water level in the chamber then rises. The increase in the chamber water level adds pressure to help clear the air from the pipe. Once enough water pressure exists in the chamber to overcome the back pressure, the air is literally is "burped" out of the drain line which crates a sudden rush of water. This is displayed as a rapid drop in the overflow chamber water level. This cycle then repeats itself over and over as the back pressure builds and gets purged.

How much water can the standpipe process? The presence of a standpipe really makes no difference in how much water you can process. The limiting factor is almost always the teeth spacing of the overflow chamber. This is what limits how much water can enter the chamber. If your plumbing can handle the water flow without a standpipe it will handle it with a standpipe. However, many people have reported being able to push the drains beyond the rated limit by increasing the teeth spacing and reducing the vent hole size which pushes the standpipe to act more like a siphon than a gravity drain. Doing this is risky and you are on your own. I can't recommend it. But people have claimed to reach rates as high as 800 to 1000 GPH with 1 inch bulkheads rated for 600 GPH.

What about the air bubbles? The vent hole in the end-cap prevents a full siphon from forming by letting a controlled amount of air enter the standpipe. This air travels down the drain plumbing and into the sump. This can be anything from a mist of fine air bubbles to a rolling boil of bubbles. If left unchecked the air bubbles can make it back to your return pump, get chopped to micro bubbles and sent to the display area distracting the viewer. The air bubbles in the sump can be dealt with in many ways such as using a baffle system, filter sock, refugium, etc.