The water level in the tank needs to be much higher than the drilled hole so that the piping flowing down to the sump is always completely filled with water. Note that a drilled tank needs special considerations if the water flow is down to a canister. But if the aquarium isn’t drilled, some sort of siphon must be used to get the water over the edge of the aquarium and into the sump. If the aquarium is drilled, then the movement of the water back to the sump can be as simple as just hooking up a tube.
There are a huge number of DIY devices on the internet and YouTube that are designed to do this.
Then there needs to be a way of moving the water back to the sump and to prevent the aquarium from overflowing. When one uses a sump the pump in the sump moves the water back up to the aquarium.
