Once the water level drops a little, siphon will break on its own, I've never had to drill ports, in Utubes
In fact the most common problem I've had is "random siphon breaks", where air gets trapped inside Utubes, and break siphon it when I was not around,
and where the pump keeps pumping spilling water on the floor until the sump is drained
(one of the reasons I learned to drill to avoid random siphon breaks.
I also tried this over flow tpye that needed suction pumps to maintain continuous siphon.
On the one above, I used a power head venturi port to assure siphon wasn't upset.
To me drilling close enough to near the tank rim is the only to manage the siphon break induced stress.
In that way, if a power outage occurs, the tank will only drain to the overflow port, and no lower.
Even though I run my sumps close to full, it usually will not overflow if the sump/tank holds enough volume.
To me this means a tiny sump is pretty much useless.
When I first bought a tank here in Panama, it come with 2 tiny sumps.
They each held only about 20 gallons, but since they were outside sitting on the grass, I didn't worry about random overflow.
So I ran them close to the tipping point.
But one of the main points in having a sump, is expanding water volume, and having enough space to add lots of plants that consume nitrate.
To me just ammonia/nitrite reduction is only a small portion of what I expect a sump to do,
once a tank is cycled the most important factor is reducing nitrate between water changes with heavy plantings.
I quicky found a 125 gal tank to use as a sump, and ditched those wimpy plastic do dad that were poor excluses for sumps IMO.
It reglarly rains enough to overflow the sump here, but I use a continuous PVC overflow to drain off excess rain to te garden,
