The main items you will need :

#1 Air stone

#2 Clear silicone tube

#3 Plastic tube

#1 - Use an electric drill to make a hole for the clear silicon tubing

#2 - insert the clear silicon tubing via the hole you just drilled

#3 - connect the air stone to the clear silicone tubing

#1 - insert a thinner plastic tube to the lower part of the 90 deg tube

#2 - connect the water inlet to the bottom of the thinner plastic tube

#3 - this is how it should look at this stage

This is a sketch of how it looks from the side

1 = Aquarium walls
2 = "white" sand = Pool filter sand ( quartz )
3 = the background decoration - with a round hole in the top ( to let the "sand" pass )
4 = water

How does it work ?

#1 - air bubbles ( in green ) are pushed from the air stone and rise up, pushing water upwards

Notice !!! that the background hole is not horizontal but goes downwards, this causes the air bubbles to go out from the back of the background !!!

#2 - sand particles are sucked from the sand pile and goes up, at the top end they are heavy so they move in the bottom of the tube and then drop back to the ground

you need to make sure that the "sand" falls to a place where the water inlet can suck it

Some waterfalls pictures found on the internet ( all rights are of the respectful owners )

Just remember - you are limited only by your imagination !

I Hope this guide has helped you, looking forward to see your AquaScaping breaking my own imagination

I will be happy to hear any feedback :)