Rather than sticking a tube down the dipstick, why not clamp a hose on the top of the dipstick tube.

This is the way my boat's inboard (Yanmar) diesel is designed. The hose fits over the outside of the dipstick tube and clamps on with a hose clamp. It works great on the boat's inboard.

This is also the way the MB shop sucker works. There's no tube that goes down the dipstick. Instead, a fitting just goes into the very top of the dipstick tube, and pressure seals off the tube so that the vacuum will work.

Not sure about the physics of this, but I suspect it gets as much oil out as any other method.