Here are two large screens that I have built with semi-rigid mesh that I acquired, I don't remember where, but I have more. Both pics below are of siphon (Herbie style) drains controlled by a valve.

The one above would partially collapse when clogged. 

Below, the same mesh as above was secured around a frame with white Zip Ties at top and bottom. The frame was made by cutting very large openings (~80% cutaway) in a 6" length of ABS (sanitary) pipe with a cap on top. Sorry, Feather Duster worms have colonized the mesh, making it hard to see the strainer itself. It's sheer size allows water to still pass freely, even after 6 years without a single cleaning. 

Aloha,

Mark  

"The Cap is sized 0.5" diameter larger than the standpipe."

In the case of the four posts the Cap is actually the same size as the standpipe, but you can see from the pic of the device at my shop that the cap floating above the standpipe is larger diameter. The larger cap allows more water to pass down the drain. In most recent instances I have glued an "X" or "Y" of thin cut PVC or other plastic spacers inside the cap to hold it above the Standpipe, it's own weight holding it in position. It is an advantage in that it can be easily removed or even pushed up or aside by any large debri that needs to go down the drain.

It would take some extensive work to make the return go up the outside back of Rich's tank to allow an emergency drain in the overflow. Without an emergency drain the tank has flooded a few times due to the small screen getting clogged that sits on the top of the standpipe above the gate valve. A larger screen would really help but the amount of hair algae in the system really needs to be addressed to make the drain screen obsolete.

Modified Durso top view. The Air Hole can be seen in the center of the cap. This was my coral farming tank in 2005-2007

Below is a pic with the Cap removed to show 4 posts that hold the cap in position, at the proper height, so water can flow under and up past the lip of the cup and then down the standpipe. Note that there is no drain screen. I have found it to be unnecessary.

As seen above, the top of the standpipe has been delicately cut away to leave four posts. It is preferred to use a bushing to run larger pipe for the top of the standpipe. The usual 1" can be easily bushed up to 1.25" or 1.5". This significantly enlarges the spillway allowing more volume of water to fall unobstructed down the sides of the standpipe. The cap is sized 0.5" diameter larger than the standpipe. The Modified Durso is more compact and easier to work with than the standard Durso and because of the larger unobstructed spillway it can handle more water and is generally quieter too. 

Here is a old pic of the Muffler/Silencer that I made for a skimmer that also works for the Durso. The longer distance of drain piping to the sump in another room or the basement means that the falling water pulls more air with it, requiring the Durso to have a larger Air Hole and a Muffler. A stubby piece of stiff tubing connects the bottom of the Muffler to the Air Hole in the Cap of the Durso device.

Here are pics of the Modified Durso on the system currently running at my shop. This is a 30 gal breeder that was previously drilled in the bottom back center directly underneath this tanks center brace. That location would not have been my first choice but it worked out well because the Cap can be positioned perfectly over the standpipe and then slid sideways periodically to allow surface scum to go down the drain.

Aloha,

Mark