No airstone, and yes you will need 2- 2 litres... You will cut the top off one, and the bottom off the other... The one you cut the top off will be your base or stand as you can see... the one you cut the bottom off will be your hatching chamber... Cutting the bottom off allows you to easily fill it and add your eggs... if you drill the hole in the cap small enough you wont even need to seal your airline going in as it will self seal.
I poked holes in the bottom that I have cut off and inverted it as a lid for the hatchery to keep out anything that may find it's way in... You can see it inverted in the pic.
It works like a champ... I just put it by the window with the airpump, nothing else no heat or light(aside from the window) in 14hrs I had over 90% hatched I would say. Hardly any unhatched eggs. Ambeient temp was 74F
My mandarin was gobbling them up 5 or so at a time... so much she was choking(or what appeared to be choking) at times. My fire fish was zooming around the tank getting his fill aswell..
I used about a 1/4 teaspoon of eggs, and I filled a 20ml syringe for the nano, and the rest of the hatchlings about 1 litre I put in a container to try my hand at gut loading them into adults. ( also got great advice on this aswell) We shall see how they go...