Lets look at the obvious points... You always want the water to drain faster than you can put it back into the tank. This way, it flows over the "dam" and into the overflow box, and then thru the bulkhead and inevitably to the sump.
Your not actually "matching" any flow rate, your more or less, deciding that you first want.... say, 12 times an hour flow thru your ank... then, we take 20 gallons times 12, and say that your pump must delive 240 gallons of water, per hour to your tank.
Next, having a pump in a sump below your tank that pumps 240 gallons per hour, wont work for you... the weight of the water pumping up to the tank and the friction in the lines, pressure and many other factors exhibit whats called "head loss" thus, your pump will have a rating that states at 0 feet, or in a bucket, a pump will pump 500 gallons (for example). If we put a pipe on the pump that is 1' long, and pump water from a bucket to another bucket that is 1' higher, we only get 490 GPH. And so... at 2' may be 460 gallons, and 4 feet may be 390, and so on...
You need to decidd how high the pump will have to pump the water.
Not all pumps are created equally. some are more expensive, use less power, and are better built. you get (for the most part, ) what you pay for.
And... no, a 3/4" bulkhead means that it is threaded for 3/4" pipe, the hole might be 7/8" or 1" for example. but I say oversize. you want water to run out faster than it comes in... the reverse would be bad. So... if a 3/4" bulkhead is 5$ and a 1 and 1/4" bulkhead is 5.50$.... Why save 50 cents... buy the bigger drain... not only that... but the peace of mind that a snail wont clog your drain line is priceless.
Jason
So if I were to take you up on your offer, and you were to drill it for me, I would first need to have the bulkhead I will be using in hand so you could drill the hole to the correct size for the bulkhead...correct? And I already know about the head loss calculators and such. And marinedepot has a table for head loss for the pump I will be using so I'm set there. I just need to figure out the bulkhead/plumbing and gph flow of that combo.
Then I spent about an hour at home depot trying to rig up a durso since they didn't have all the pieces I needed. And I'm still missing one. Unless I want an internal overflow box that is 6" front to back (tank is only 12" front to back), I'll have to look elsewhere for a 90 degree threaded street elbow in 1.25". 
Or pay $8 for one online! :mad2: I don't really feel like wasting a tank full of gas driving to every parts store in town. Anyone know of somewhere in town that has a better selection of pvc fittings than home depot?
