Combo help

[Batmannn]

I'm trying to cancel or link a slash kick after the 3rd hit of Joe's rush combo as seen in this vid at 00:58 mark:

https://www.youtube.com/watch?v=fmSfpD4ZMtM

I can't make the slash kick come out after that standing knee attack part.

Any suggestions or recommendations would be greatly appreciated!  Thanks! 

[Vokkan]

Dude, the slash kick is the 4th hit of his Rush combo