How to flush electric engine tilt hyrdraulic fluid?

[dalfordiv]

I need to flush the old oil out of my unit where you put the hydraulic fluid for your electric engine tilt.

I know how to add fluid by removing that big knob but I don't see a drain screw or plug that I can pull out to empty out the old fluid.

If it matters, this is a 115hp Yamaha 2 stroke outboard. Any help would be greatly appreciated.