I've done it two ways.
Had a Brownie's Third Lung, which had a gasoline powered compressor, worked to 35 feet, and would give you about three hours underwater time.. Used that when I was doing salvage diving work,, some 30 years ago. Tank and a half of gass was all the underwater time I wanted in one day!!
Lately,I've worked under using an electric compressor and one of my Hookah regulators, hose and surge tanks. That works very well, as long as the boat is close to an electric outlet-grin
If you DO use one of the electric compressors, make CERTAIN it has an oil less compressor. Oil forced into lungs under pressure can result in a very nasty form of pneumonia. Also,, as long as you go no deeper than one atmosphere (33 feet) you should not have to worry about decompressions, in the times your body will stand being in the water-Grin