I use a old squash bottle the large 5ltr square one with the end cut away the screwtop end then fits on my shopvac but thats only a 1 3/4" hose so I don't know if that helps you much.
In true Blue Peter style, I made one out of a cornflakes packet and connected it up to my shop vac using the top of a plastic coke bottle. It worked OK but demonstrated that my vac was too noisy and too wimpy, to be a serious contender. I was still wearing a mask and now I had to put on ear defenders...! So I invested in a Camvac and will be setting it up in a couple of weeks - just as soon as I've finished the kitchen!