In a few simple steps, you can make your own bottomless tank that your fish can swim in and out of.

It's a striking, above-water aquarium that fish can swim in and out of. And unless there's a leak or jolt to the aquarium, there shouldn't be any implosion and resulting flood in your house.

The principle behind this awesome aquarium trend is that the pressure at the top of the inverted "tank" is much less than the pressure at the bottom and less than the atmospheric pressure. The water will not leave, especially if all the air has been sucked out.

Please note that this idea requires the usage of a dremel tool and plastic will be burning/flying so work in a well-ventilated space.
Also note that since this is not aquarium safe plastic, this may or may not kill your fish. Please use some test fish first or something.

Okay, let's get started.

Step 1: Materials and Tools

Materials

2 plastic bowls, trays, etc... in which one can fit on top of the other. Look in the vase or tupperware or cup/bowl section of your local supermarket. There's rarely any clear buckets. Ideally, one should be more bowl-like and the other more tray-like.

Whisper Filter. The gentlest one will be fine, that's what I used. The more power, the fast it'll go. It'll be modded into a pump.

Air pump.

Airline tubing. Enough length for the end to reach the top of your inverted bowl, though the access hole, and to your Whisper Filter.

Test fish. Cheap shrimp or fish.

optional: plants, gravel, ornaments, airstone.

Tools

Dremel tool with cutter attachment. optional: grinder attachment.

Rough sandpaper.

Small cross-head screwdriver.

Needle nose pliers.

Measuring Tape

Marker

Towels.

Water.

Electricity with at least 2 outlets.

Plastic fork or knife or spoon or styrofoam curly.

Rubber band.

Step 2: Set Up Aquarium

set up all your stuff in the tray of the aquarium exactly the way you want it before you start.

it's very difficult to adjust once the water's in. you'll have to empty it out and redo it.

if you have live plants, they can survive for the 10 minutes it takes to fill up the tank.

note that gravel, especially fine gravel, will be moved around if there's a sudden change in pressure.

NO FISH. It's might scar them for life.

Step 3: Drill the Access Holes

Drill access holes for the fish to swim in and out of the bowl of the aquarium into the tank of the aquarium.

The more holes, the more access and more water flow. But the more holes, the more the bowl is weakened and may not support the water. I drilled 2 for symmetry.

Mark with a sharpie the rough shape of the hole (circle, square, triangle, etc...)
The hole must be large enough for a fish to swim through: 1 inch by 1 inch is good.
Be sure not to drill to high or the water level of the tray will have to be higher to prevent air from escaping into the bowl and lowering the pressure and causing overflow.

Cut out the hole using the dremel tool.
try not to let the attachment "skip" on the glass or make extraneous cuts.

Smooth it out using the grinder attachment if you do.
Regardless, use a rough sandpaper strip to smooth down the edges of the holes.
Run your finger along the edges and the corners to feel the sharpness.

Remove the burrs with water and towels.

Step 4: Make the Vacuum Pump

Go to Random_Canadian 's instructable on how to make a vacuum pump from an air pump.
https://www.instructables.com/id/Vacuum-Pump-from-Aquarium-Air-Pump/

Despite their modesty, it gets the job done well.

Be gentle with the bellow drive-shaft thing.

Be aggressive with the white plastic thing.

Step 5: Filling It Up/Down/All Around

Place the tray near a sink and water faucet.

Place the bowl upside down on top of the tray.

Fill with water until the tray's water level is much greater than the height of the access holes.

Hook up the vaccum pump to airline tubing.

Attach the end of the airline tubing a fork or long stick thing.

Wiggle the end of the airline tubing through the access hole to the top of the upsidedown bowl.

Turn on the vaccum pump.

Step 6: Notes on Filling It Up

Be sure to keep the water level of the tray above the access hole. Air will seep in and the process will take longer.
Periodically fill up the water level of the tray.

Always keep the end of the airline tubing above water level. Water will travel into the vacuum pump, causing noise and probably some problems. Then you should spray out the water in the tube with the air pump, which increases the pressure in the bowl.

You should see the water level of the bowl rise and the water level of the tray fall.

In the photo, I used a sponge to float it. It sank. I then used a fork.

Step 7: Nearly at the End

When there's barely any air left, refill the water level of the tray one last time.

Position the tube end against the top of the bowl.

Then let the vacuum pump take out all the air and a little water.

Air left in the bowl will stagnant, necessitating periodic air changes. Besides, the fish can go out into the tray for air.

To remove the water from the vacuum pump, remove the casing.
Turn the pump upside down on top of a towel.
Rapidly press the level up and down.
Shake the pump to hear if there's any water left. It takes some time for all the water to leave.
Then screw the screws back.

Step 8: Optional Stuff

You can add an airstone in the tray to increase oxygen exchange in the aquarium.

There's no heater, filter, or lights. However, if you could possibly make a water bridge to another fish tank and "borrow" their water.
Or you could look at my other instructable and make an external drip filter. If so, please note that both the intake and output water tubes do release air with the water so putting inside the bowl is a bad idea.

But first, add some test fish or shrimp to make sure the water's safe.
Because the plastic is not aquarium-grade and has been ground, cut, and melted by the heat, chemicals may leak out.

If you're thinking of making a betta bowl, please use at least 2 gallons with a heater that regulates at 78 degrees F.