Simple, a wall that you can control the volume to with the sliding of your click mouse

could be controlled by the same thing that controls the fan tool.

you can control the amount that comes out in a pipe or what ever.

it must be drawn with the Shift Clickhold tool, which means it must be linear, and can be drawn in any desired direction,

and maybe a snap tool to lock onto the end pixels of a pipe or something

ok well heres the idea:

I have a pipe and I want to control how much goes through this pipe at any given time.

or:

I have this stove, the flame is too much so I want to make this lower without having to draw more of anything