I'm installing an automatic water change system on two 10 gallon aquariums. This post will cover how I set up the overflow drain system. See this post about drilling the tanks for more on installing the bulkheads. You can see the overflows installed on the tanks below.
Once the bulkheads and overflows were installed in the aquariums I assembled a drain manifold to mount on the back of the rack. The manifold is built from 3/4" PVC, and connected to the overflows using 3/4" braided PVC tubing. It is mounted to the back of the stand so none of the components are visible from the front.
The manifold has two slip x thread tees that allowed me to thread in hose barb attachments. It also has a vented standpipe at the end to allow air into the system so that water can drain without creating a siphon. The cap on the standpipe has a 3/8" hole drilled into it for air flow. After dry fitting everything, I glued all of the connections except the cap. The threaded connections were made using plumbers tape.
The PVC drain assembly runs into another section of braided PVC tubing, again using a thread x hose barb connection. Plastic pipe hanging straps suspend the line at the right height for each section so that it has a consistent slope. The end point of this line is about 17" inches off the ground, and the bottom of the aquariums is at about 21". The total length of the line is 12 feet. So I have a consistent 1/3" drop per foot, which meets the local plumbing code minimum of 1/4" per foot.
The drain line then runs across the room and connects to the drain of my utility sink. I used this branch tailpiece to make that connection. This allows the aquarium overflow drain to use the sink's P-trap. The branch tailpiece has a hose barb for 3/4" tubing, I just slid the tubing over it and used a hose clamp to keep it in place.
Now I'm in the process of setting up the two tanks attached to this drain system. So far I've run quite a bit of water through the overflows and haven't seen any leaks at all. There shouldn't be any failures because the system is a passive vented drain, so its not under any pressure.
I'll be posting a complete walk through of both 10 gallon setups as soon as they're ready. Currently the plan is for one to be a new home for my cherry shrimp colony, and one to house my male betta. Bothwill be planted tanks running a setup I've never used before, so the results will be interesting.