I'm sure many of you with drilled tanks have some method of quietening the drain from the tank to the sump. One of the best known methods is the Durso Standpipe. I built one to go in the overflow box of my tank but decided it could be improved.
There seem to be 2 main reasons for putting a Durso in your tank. The first is to reduce the noise of water gurgling as it goes down one or two metres of pipe to the sump, sucking down air with it and generally being noisey. A second reason for those of you with overflow boxes in your tank is to raise the water level in the overflow box so water isn't making a noise as it falls the height of the tank to the drain hole.
If you have a Durso Standpipe already then you will know it solves both of these problems. But not completely. Mine would periodically make gurgling noises and then settle down again for a while. The air hole in the top cap would become blocked by salt which would also stop it working silently.
Having easy access to the boxes of plumbing parts in the Fish Fur and Feather warehouse has encouraged me to experiment and modify my Durso. I've tried longer pipes between the T-piece and the top cap. I've tried different diameter pipes. I've even taken the top cap off and put a clear plastic bag over it so I can watch how the water flows when the top is blocked (don't try this unless you want be pulling a plastic pag out of your drain pipes). Nothing seemed to have a significant effect on the Durso's behaviour.
One day after using some air hose on another project I was watching the Durso wondering if there was another way to get air into the pipe without it gurgling. Having about 30cm of air hose in my hand, I stuffed one end up into the Durso entrance, around the 90 degree bend and then pushed it down the main pipe until the end was about 10cm below the bottom of the T-piece. The exposed end should be kept above water level. Fasten it to something or else the whole length will get sucked down the standpipe (experience talking here). I then blocked the hole in the top cap of the standpipe. The pipe 'cycled' a couple of times, draining down the overflow box and then refilling, and then settled down. And has been silent ever since.
As you can see from the picture I have jammed my air hose into one of the gaps of the overflow weir to stop it getting sucked into the Durso. I have a 32mm Durso draining into a 25mm bulkhead and using standard airline. Of course what works for me will need slightly different settings for someone else due to factors such as pump type and power, the head the pump has to pump against, pipe sizes, tank depth, etc, etc.
If you try this or have any other suggestions on improving a Durso please let us know.