Weird....it's like in Google the 1990's never happened.....all the good guides to DIY overflows were made back then....now all you see via the algorithm is retrograde stuff on video like the above. I'd be willing to run one of those if my tank was outdoors, but that's it. (And I wouldn't like it.)
Since you asked, nobody "needs" a sump any more than they "need" a fish tank in their house. Both are elective. Both can make things nicer.
I Think You Need A Standard Overflow Box
A standard U-tube style overflow box is your basic unit for getting a sump working with a standard (no holes) display tank. No drain setup is more tried and true as folks have been running these *at least* since the 1980's. Eshopps, Pro Clear, Lifereef and probably others still make them (eg):
With this you get an adjustable weir (the part in front with the teeth) that prevents blockages and sets the display tank's water level.
You get a clear U-tube for the siphon so you can tune the flow correctly. Flow can't be too low or bubbles will slowly accumulate in the siphon eventually breaking the siphon. With this setup you will see them accumulating well before there's a chance of breaking siphon so you can correct your setup.
In the back you get a drain box with a stand pipe. The stand pipe and the front weir together hold the water level of the overflow box above the siphon tube ends, thus maintaining the siphon through power outages and other system shutdowns.
The whole system works on gravity, so once the siphon is setup up and the flow rate is correct they are virtually bulletproof. A mesh covering for the weir and teeth is called for if you will have snails breeding or algae mats at risk of getting to the drain. Just the teeth are good for most "clean reef" situations, but many reefs aren't "most situations". So extra protection is possible. (My buddy does this on all his drains no matter what style they are. I have never done it. Depends what you're going to be doing in the tank.)
The water flow rate from your return pump is what sets the flow rate through the drain box. Again there has to be a minimum flow rate to keep bubbles from "settling" at the apex of the U-tube....and you'll see whether you've got it right or not. In general, a 1" drain setup is good for a maximum of 600 GPH, but will be silent only up to about 50% of that flow....so about 300 GPH should be close to ideal, and should keep bubbles from accumulating as well.
For a tank this size, if flooding or leaks are of utmost concern, you should also consider alternatives. Like running an
in tank filter system like a Tunze 9004 protein skimmer + Comline filter. The filter unit is also a place for your ATO sensor and heater to be hidden. Using just the 9004 skimmer (without the Comline) is probably fine if your bioload will be moderate.....having a low bioload is a good idea in general.
I hope this helps!
