How do I use a sewer donut?

Seems like a simple enough question I know. But I don't know the answer and I'm curious.

YEARS ago (2006), I booked a full hookup campsite just to see what it was like. It was my first full hookup ever and I was, well a bit excited. I could use all the water and electricity I wanted. :) Anyway I thought I'd hookup the slinky as it I wanted to try out everything about full hookup.

I figured the proper way to hook to the sewer was to slide the donut onto the smooth attachment at the end of the slinky, and then put it down the hole. But the donut wouldn't fit in the hole. :h In the end I just put the slinky away and only pulled it out when it was time to dump.

Since that day I have never left the slinky hooked up unless it was time to drain the tanks. This wasn't really because of my donut experience but it's just the way I do it. But I've always wondered what I was doing wrong.

So my questions to you all is "how do you use the donut"? or what was I possibly doing wrong?
Am I supposed to put the donut on the slinky and then in the hole?
Or was I possibly supposed to put the donut in the hole and then force the slinky into it?

Thanks