Durso Standpipe...

A common problem with overflow boxes is the noise they create if not modified. The noise is a result of the water flowing through the overflow teeth and crashing all the way to the bottom before exiting the drain bulkhead. A common solution to this was to add a simple standpipe, which raises the water level in the overflow box. If left as just a standpipe with no modification, this will produce an awful sucking noise similar to a bathtub sucking in air as it drains when the water level drops low enough to produce the little "tornado". Solutions to this were often drilling many holes in the standpipe to allow water to enter it at all heights, with the goal being to keep the water level high but with enough holes so that the water did not go over the top of the standpipe. This is nearly impossible, and very time consuming.

There is a simple, easy, and economical way to fix this problem, and it works great. Commonly called a "durso" standpipe, it is a standpipe that uses a submerged intake to keep it quiet. This eliminates the need to drill all those holes in the standpipe, and also eliminates the terrible sucking noise. It can be built out of regular PVC parts available at any hardware store.

This is a durso standpipe as it would appear inside an overflow box from the rear. The water level in the standpipe should run at roughly the mid section if the tee when in operation.
This is the top detail of the standpipe. The arrow is pointing to the hole that MUST be drilled in the top of the standpipe for it to work properly.

There are a few things to note before building the standpipe(s). One is the selection of the PVC size used in the construction. For tanks with a 1" drain bulkhead, you should use 1.25" PVC parts. A reducer bushing will be needed at the bottom of the standpipe to fit it to the 1" bulkhead. For tanks with a 1.5" drain bulkhead, you can simply use 1.5" PVC parts. Also, use inexpensive, thin-wall PVC in the construction, as it has a greater inside diameter, which can handle more volume. The desired height of the water in the overflow is roughly 2" below the overflow teeth, and does not need to be exact. Keep this in mind when cutting the main standpipe section, #5 (see photo below). Also, since space in an overflow box is limited, the 90 degree fitting, #4, should be what is called a "street ell". A street ell has a female end that fits directly into the tee, #3, and saves space.

The one disadvantage of a durso standpipe is that uneaten food, sludge, etc, can accumulate in the bottom and sides of the overflow over time. This is a minor problem, and really not a big deal. But for this reason I recommend using all slip fittings in the construction of the standpipe, and not gluing the standpipe to the bulkhead. If left unglued, when the interior of the overflow accumulates too much sludge, you can simply scrub around inside the box to loosen things up and pull the standpipe out of the bulkhead. Everything will flush out and you now have a clean overflow. Simply push the standpipe back in until next time. Depending on what kind of filtration you have, you may want to have some way of collecting what is flushed out so it does not end up in your filtration. Also, turn the tank pumps off while cleaning out the overflow box so water is not coming in when you pull the standpipe.

Building the standpipe

1. Cut a small section of PVC (#2) and attach the endcap (#1) to the tee (#3) using this small section. 2. Attach the street ell (#4) to the tee (#3). Point the ell directly downwards. 3. Cut the main pipe (#5) so that when inserted both into the bulkhead (#6) and the tee (#3), the mid section of the tee will be about 2" lower than the overflow teeth. 4. Attach the main pipe (#5) to the bottom of the tee(#3). 5. Glue the whole apparatus together with regular PVC cement. 6. Drill a small hole (start around 1/16") in the top of the endcap. This will prevent a siphon from draining the overflow too fast, and the size of this hole may need to be adjusted. 7. Push the standpipe into the bulkhead, (#6). If satisfied with the height, turn the aquarium pump(s) on and watch the water level in the overflow. If it maintains a steady height at roughly the mid-section of the tee, you're done. 8. If the water level in the overflow drops too far, you will need to increase the size of the hole on top slightly. Make the hole bigger in very small increments until the water level in the overflow maintains its height at the mid-section of the tee. You can also install an air valve in place of the hole and simply turn it until the amount of air coming in is correct.

For a more complete description of the durso standpipe, common modifications, etc, go to...

www.dursostandpipes.com