To achieve a "constant height of pond" (CHOP) in my bigger tank, I needed to install pipes to let water flow down to the sump.
I used 3/4" pipes to plumb through the tank walls, because that way I could get away with using the 1" drill bit. I drilled two holes near the top of the tank, in the recessed 'ribs' so the piping wouldn't stick out as far. If I was doing this a second time, I would locate the holes a couple of inches lower, but this works.
Once the two pipes coming from the fish tank join, I transition to 1" piping, to make sure flow out of the fish tank isn't restricted by the plumbing joining the tanks.
[After I already had the fish in the tank, I realized I would have to turn the tank so the side with the ribs close together faced the sump. Not sure the fishes liked having the water drained down to almost empty, but I was glad to be able to move the tank without having to net everyone out.]
The 3/4" pipes in the fish tank extend down to the bottom, forcing water from the bottom of the tank to flow out of the tank when the grow beds drain into the fish tank. I drilled a pattern of 13 holes in each end-cap and cut small slices at the very end of the pipe with my miter saw. This allows enough flow through the bottom of the pipe so water drains well (else the fish tank could overflow). The reason to use two pipes is so drainage can still happen even if one pipe gets blocked.
This picture was taken before I actually plumbed the two tanks together, so the 1000 gph pump is still in the fish tank. I used regular 5/8 hose and a garden hose splitter. Turns out 5/8" no-kink garden hose and regular splitters work fine - they are inexpensive and come with built in ball valves. After these pictures were taken, I replaced the green hose with white hose that is lead-free and certified safe to use with drinking water.
Once I get to the sump, I transition back to 3/4" pipes, again so I could get away with my 1" drill bit. You can see the 45 degree joint that lets the water from the grow beds and fish tank flow into the sump with minimum noise.
I've been running the system for almost a week since these pictures were taking, and it works just fine.
For the record, here's what the grow beds looked like when I plumbed the tanks together.
I ended up adding hydroton to all my beds when I couldn't coordinate getting the expanded shale delivered before my fish had to be bought. Too much travel, between spring break vacation and work trips.
Even though I would have preferred the expanded shale, a nice thing about the hydroton is it is distinctly different in color and shape from couple inches of gravel from my original system in the bottom of each grow-bed.
In the week since these pictures were taken, I've shifted the pump to the sump, invented a way to keep the water topped up, and built kiddie covers for the tanks. But I'll cover those items in future posts.