The bubbles bring everything up to the surface to exchange stuff. One could probably skip the bubblers if their solution was 1/4 an inch deep with a surface area of a football field.

Not claiming I have ever actually made any.

You can make tea without an air-pump, however it will not be as good as aerated tea.

I have mixed my ingredients in a 5 gallon bucket and filled halfway up. Then 3-4 times per day (or more) dump the contents into another bucket and transfer back and forth 7 times. This is how painters mix paint. It gets some air into the mix. Use luke- warm non-chlorinated water.

Good luck!