Hi,
Not sure about autocad, but in DeltaCad I made the wavy line using the spline function. I make the first point of the spline at the end of one side of the pipe, the second 1/4 of the way across and the same distance beyond the end of the pipe, the third 1/2 way across flush with the end of the pipe, the fourth 3/4 of the way across and the same distance before the end of the pipe and the fifth at the end of the other side of the pipe. This will give a wavy line across the end of the pipe as shown in your drawing.
I presume Autocad lets you draw splines.
It’s a shame DeltaCad bit the dust. It was the easiest drawing program to use if you had learnt to do technical drawing on paper. When all is said and done, all you really need to do is draw straight lines (vertical, horizontal and angled), circles around a given centre, splines for ellipses and to dimension the finished drawing. Everything else in Autocad only makes things quicker while making them too complicated to use.
Regards,
Alan C.