To answer your question, I built the base to the airlifts from the necessity to have them stand upright in the tanks. ( I run one in each of the two fish tanks.)
Whenever i secured them to the side, they would rattle against the sides and drive the fish crazy, or they would just fall over or float.
So, I built the bell out of 100mm left over pipe and caps, placed the lift inside and filled the whole thing with scoria to keep it weighted down and upright.
What you cant see inside the bell is at the very bottom there is a 40mm cap into a short 40mm pipe that have 4x4mm air hoses inserted into it, then that piece of pipe is pushed into the 40mm T piece that you can see poking out of the bell then on and up to the elbow and outlet.
Works brilliantly. The difficulty for us to get good lift is that our tanks are only 750mm deep, and over coming good head height at shallow water levels was the biggest issue.