In response to Loh Kwek Leong's guide on how to create your own hatchery, I must say it's pretty effective during harvesting. If you are worried about the sunken unhatched eggs, do not fret. Only a little unhatched eggs will be accidentally harvest. The diagram below will help you understand why.
As you can see, as long as the amount of unhatched eggs is below the air valve, only brine shrimps will be harvested.
I suggest using Thread Seal Tape (the white tape that plumber use to seal pipe joints) to seal the air valve. Although the guide said that no water will drip, I found it untrue. Vibration from the air pump will dislodge the connection and water starts dripping.
One advantage of using seal tape instead of silicon is that the air valve can be easily removed to fit on another cap. Silicon will most likely seal the air valve to the cap.
Second advantage, no need to wait for it to dry, just warp the tape around the air valve and screw it in.
Third, if you make a mistake, just re-warp and you are ready to go again. If you make a mistake with silicon, you will keep applying more silicon, making a mini-hill at the end of it all.
Depending on your situation, you can either do as the guide said and hang your hatchery or create a stand for them. Just cut out the top of another bottom and leave the hatchery on it.
Conclusion: Great DIY hatchery. Save lots of time. Very effective during harvesting.