Overflow Box Pipe Fitting/Bulk Head question

[W_Oz]

I'm setting up a DIY sump system for my GF's 10gal soon to be planted "Bamboo Forest" tank. I have the sump itself in the works, just deciding which Rubbermaid tube I'm going to use, but I've also built a small overflow box from some scrap plexiglass I had and I've run into the problem of just how big of a bulkhead I'll need. The pump in question is a submersible pump that I've been using to help with water changes on my aquarium on the refill side but it's small and is rated at 90gph max. I doubt it actually moves that much water, but what the heck it'll be more than enough to get the job done.

So my question is this, just how big of an ID do I need to get upwards of 100 gph moving through this box? Originally I was thinking of just using some 1" bulkheads but it seems that those will be overkill, not to mention difficult to find hose to fit over a barb fitting of that size. I see that the boxes on eBay with a 1" bulkhead drilled in them are rated at 600gph (WHOA!) and I know that I can't just go and shrink the fitting in a linear fashion but I can't find a good calculator to tell me how big is "big enough". The one I'd originally based my choice on was for a waterfall spillway which stated that a .8" square spillway would flow at around my target 100gph (a little more actually) which has about the same x-section area as a 1" Sch 40 PVC pipe.

So, what size ID do I need to move 90gph under the influence of gravity?

Edit - Anyone know where I can track down a piece of that U piping as well? I'm not coming up with anything in my feeble attempts to get the internets to give up their secrets. :ssad:

[W_Oz]

Apparently not? Bummah... I suppose there's always trial and error... but I'd like to avoid the "error" part :19:

[ILuvMyGoldBarb]

First question is how high do you have to pump the water to get it from the sump back to the tank? A 90gph pump may not be able to handle it.

[W_Oz]

The pump itself regularly moves water from effectively ground level to ~48" high during water changes. Besides, the overflow box can be more than capable of much higher flow rate than the return pump, and should be capable of a higher flow rate simply from the standpoint of safety to prevent an overflow in the tank if the pump is capable of an excess of it's rated gph.

Technically there's nothing wrong with having a bulkhead fitting on an overflow box that's capable of 600gph when the return pump is only rated at 90. I could build it so the box has a 1200gph capacity. The problem is one of convenience. Since it would be nicer to have a bulkhead that I'd be able to use a commonly available tubing size as opposed to needing to use "hard lines" to get water from the box to the sump.

The reason the flow rate of the overflow doesn't "matter" is because it will only remove water from the tank at the same rate as the water being returned to it. If I just had a siphon line in the tank then I'd need to worry a lot more about how much water would be leaving the tank vs. the pumping capacity of the return because if the pump isn't pumping as fast as the siphon is draining then the sump overflows all over. Or if the opposite happens and the siphon can't pull enough water fast enough to the sump, the pump would run dry.

My goal is to have the overflow box be capable of keeping up with, say 120%-ish of the max output of the return pump. This would allow the use of smaller plumbing, which means it'll be cheaper to build and allow me to use a vinyl/silicone hose.