What does the average 300 gallon 8 foot tank come with ....how many overflows and how many drain/returns.....
It all depends on how much flow you want through your display and sump and how you're setting up the drains. Personally I like a fast flowing sump. It keeps detritus from accumulating and brings new water in to be cleaned rather than cleaning the same already processed water.
From the research I've done on my 300 build I can share this.
Beananimal's design is virtually flawless so that's what I'll be setting up. Coast to coast is going to give you the best surface skim and that's what we're striving for.
First I determined how much flow my return pumps would generate. For me the Waveline DC12000's produce 2000 gph at 5 feet of head. To me that's not enough as I think a good rule of thumb is 10x the display. So to add more flow and for redundancy I'll add a second pump. Now I'm at 4000 gph. A little more than 10x, but that's ok. To get maximum efficiency from any return pump you should use whatever thread size it comes with and try to limit bulkheads, elbows, etc. I'll be using vinyl tubing and go up and over the overflow.
As for the size of the overflow itself. You can use
RC's calculator. For me at 4,000 gph I need 60 linear inches of overflow. Keep in mind If you add teeth to the overflow you're cutting it in half or pushing the water level up and not getting a thin sheet of overflow. This can be fixed by adding plastic gutter guard.
Now back to the beananimal drain. Using his calculator I determined that at 42" of head on a full siphon 1.5" pipe would flow 4966 gph. But of course having the gate valve I can dial it back to the 4000 gph to match the returns.
Make sense? So for any setup, figure X times volume and match the pump. Use RC's calculator for overflow width. Use Beananimal's calculator to determine what size bulkhead. And you'll have your answer.
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