The tank originally comes with the 2 internal overflows. The drains are 1" durso's and 3/4" returns. I want to go with the herbie design though.
On my existing system I was stuck with existing holes and am actually running a 1 1/4" full siphon but at the bulkhead it reduces down to 3/4". I had originally run the 3/4" all the way but it couldn't keep up to the flow demand. That's when I used bushings to increase it to 1 1/4" on both sides of the bulkhead and it ended up being a bit overkill. My gate valve is probably only about 25% open.
So on this tank I'm thinking of using the 3/4" holes for my siphon but increased to 1" on either side of the bulkhead and use the 1" holes for my safety drains increased to either 1 1/4" or 1 1/2".
I really don't like the over the rim returns on my existing tank so I'm thinking of drilling 3 or 4 - 3/4" returns in the back of the tank. I did this with my cube and really like the results - it looks nice and clean. I've been able to drill the MIP-Locline adapter and have no issues with back siphoning when the power goes out. But it is only a 20 gallon cube, not a whole lot of pressure. If I drill the 3/4" holes as high as I can get them (which is roughly 1/2" down from the black plastic rim on the top of the tank) I'll be about 2 1/2" down from the top of the glass to the edge of the hole. And I was originally thinking 4 holes, 1 on either side of both overflow boxes. But I suppose I could get away with only 2 holes on the right side of the left overflow and the left side of the right overflow. The factory returns come with a splitter on them so in essence there is 4 returns anyway. Anybody see any issues with drilling that many holes? Or should I just go with the 2?
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