The trick with the sump drain I think is to have it as high as you can. Mine is above the height of the baffles, and as close as I'd dare to drill the edge of the glass. The difference between the maximum level, and the minimum operational level allows the system to restart. In your case we can assume maybe 15l of water from the tank, plus the contents of the overflow box (down to the level of your lowest stand pipe).
I've got 2 outlets on my sump as I intentionally flood the sump from a standpipe within my tank for a weekly 50% water change. On an old design I did have only 1, but it sometimes got a little close for comfort if the tank was draining quicker than the sump. I've also got the pipe into the sump coming into large pond filter sock that is taller than the water level within the tank. I had found before that debris such as leaves or snails could otherwise find their way into the drain and cause an issue.
Your system would normally have water coming in a lot slower, but in a power cut situation you may find if your overflow pipe from the tank is a similar size to the drain in the sump, it could fill up quicker than the drain can take it away.
![1615852575456.png 1615852575456.png](https://www.ukaps.org/forum/data/attachments/164/164934-9f29f90885b1cf0a632f6e4fd7218251.jpg?hash=nyn5CIWxzw)
I've got 2 outlets on my sump as I intentionally flood the sump from a standpipe within my tank for a weekly 50% water change. On an old design I did have only 1, but it sometimes got a little close for comfort if the tank was draining quicker than the sump. I've also got the pipe into the sump coming into large pond filter sock that is taller than the water level within the tank. I had found before that debris such as leaves or snails could otherwise find their way into the drain and cause an issue.
Your system would normally have water coming in a lot slower, but in a power cut situation you may find if your overflow pipe from the tank is a similar size to the drain in the sump, it could fill up quicker than the drain can take it away.
![1615852575456.png 1615852575456.png](https://www.ukaps.org/forum/data/attachments/164/164934-9f29f90885b1cf0a632f6e4fd7218251.jpg?hash=nyn5CIWxzw)