According to the parts diagram, at Kawasaki.com, it's a breather tube.

It's been a while, but I think there is an outlet for it on or near the oil pump, which is at an angle of about 45 degrees. It's the only one in there that isn't horizontal or vertical.

The rubber hose just pushes in, and the rectangular rubber bit holds it in place when the sump is fitted. I think the rectangular bit ends up vertical between the block casting and the sump casting.

I think I had to cut mine down to fit the lower sump height. And instead of cutting it off flat, I cut the end off with a slash cut so it would still flow (either in or out) if I'd left it a bit long.

It's been a year or so since I've last had the sump off the car, so some or all of that may not be entirely accurate!

Thanks Ginness,
I found the hole 45º to fitt the rubber hose and as you said, now is longer than the new oil pipe, I'll cut this side to be placed over the oil pipe, just leave the end free because there is no other hole on the oil pipe to fitt it.
As Rod Ends said, if its a breather tube, is it blowing air into the sump??

Xisco