Could a 1/4" air line not be made out of ridgid tubing so it doesn't have to stick up in the air so much. I see that all tanks are done with this flex line but I'm curious as to wether or nit this is essential.
You could use a 90 degree fitting on top.
Are you asking if the kind of line is essential, or the line itself ?
If you're asking about the kind of line, it doesn't matter what you use.