I have to say I had the unfortunate need to use one of the bags on one occasion. For some reason I just got motion sickness on a CRJ into a regional airport into the US and it got the better of me. At first I was fine but the stream kept coming and I can assure you that my stomach certainly has a higher capacity than the receptacle. In the heat of the moment I didn't know what to do and it formed a stream right onto the elderly lady seated next to me to my utter horror.

She was not a very happy passenger, but thankfully had spent a career as a nurse so was much less phased than I could have reasonably expected.