You have to gently press the filter into the stem, blue cap towards you, in order to set it in place and ensure there's a seal and that the thing won't rattle. That's by design. You can't just throw it in there. I used to do the same thing and the rattle drove me nuts; then I read the instructions and slapped myself a bit with a large trout.
I tried gently and not so gently pressing the Dr. Perl filter into the stem every which way trying to seat it into the supposed conic stem many times, but nothing. Maybe I had a bad one, maybe just me?
If you use the adapter instead, you also have to gently press it into place like a filter. Again, that's by design, and that's why non-Vauen adapters, which lack the rubber inset ring won't work: you won't be able to secure them in place and they'll rattle and let smoke pass all round them.
Ditto the drilling: it's
not wrong/poor drilling: Vauens' off-centredness is
by design as well.
I had a straight Canadian not a bent stem pipe. Was referring to the draft hole entering the bowl off to one side, not in the center, when looking straight down into the top of the bowl. It was also drilled low, but that's open to debate as some makers deliberately drill low (ie. Il Duca) but is not to my liking. In the end glad it went away, as I posted in another post, if all of the air/smoke goes through just the filter, it reduces the draw more than I like anyway. Thank you for your reply.
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Vauen adapter (note the rubber ring that creates the seal when the filter is pushed into place):