I couldn't find any more used overlows for my tanks so after Googling DIY overflow, this is what I ended up making.

I used PVC schedule 40,one inch diameter, nine 90 elbows, one "T", one 1"connector, and a 1 1/4" conector that I slotted and screened.

I also used an airline valve to insert in a drilled hole in the top "U" going over the tank top.

*****I have revised the inlet piece to the ABS style described near the bottom of the page for the second unit I built.

I found the flow wasn't up to what I needed so I "lowered" the "T" section. The greater the distance between the top where the water overflows into the unit, and the "T" where the water flows out, the greater the flow out of the tank.


Upper View

In the picture on the right, the right hand part with the screen fits into the tank and the upper "U" piece sits on the lip of the tank.

This picture below shows the part that goes into the tank, in the front of the picture.

In the above picture, the left side is looking at the outside portion of the overflow that sits outside the tank, going to the sump.

This next picture is of the screened overflow inlet. This ended up being too small so I changed it to one shown below

This picture is of the valve cemented in a drilled hole in the top "U" that sits on the wall of the tank and is used to suck air out of the tube to create the suction.
Behind that "U" section with valve you can see the open upright tube that prevents all the water from being sucked out of the siphon tube if water stops flowing into the overflow.

These are some pics taken after installation.

One is a full view of a 20g with 10g sump (too small for seahorses) and the others are closer up pics of the "U" tubes, overflow, and bleed valve/air vent tube.

The black painted ones are for my seahorse tanks.

I've made up many more and while they're basically the same, I've changed the actual overflow inlet and painted it with black laquer.

Instead of the PVC 1 1/4" connector cut for screen, I used an ABS 1 1/2" to 1 1/4" reducer in the small end of an ABS 1 1/2" to 3" section that I cut and screened.

I have three of these units on the go now and they work just fine. Just remember to bleed the air out once in a while with the pumps off and no flow going through the tube