Here's how to do Yabbut. In step 5, note that the small black squares co-ordinate with the black triangular areas already created; they make the third point of the triangle.
There's a tile that uses Yabbut in my 'Walking the Line' post here. Here's another example:
|Tangles: Dex, Drupe, Hibred, Knightsbridge, Up and Across, Yabbut|