about a year ago, I ran out of vac pump mufflers, and there were a couple of folks (I think from this NG) that wanted one and couldn't get one from me - I found a small pile of them again, so if you want one, browse to my web page (below), click on vacuum pumps and take a look.
I suspect the plastic thing was a vac resivoir used on the input side, and a sort of muffler on the output side - if there were two of them - it might make the pump a bit quieter, but so would a length of garden hose taking the exhaust outside, or just winding it around and blowing it back onto the motor for additional cooling. I'd run the test for you, but I don't have any of these piston pumps any more - the first batch I had came with similar piston pumps, so they must be effective --- my solution was to put the pump some distance away from me (and then to discover that I had mounted in a way that made a drum and actually amplfied the sound....) - if you do that right, you can make it very quiet - put on the other side of the garage or something......
anyway, the short answer to your question is "probably, but I don't know for sure"
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