It's not sarcasm, it's ABRASIVENESS, there IS a difference
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Sorry if I didn't answer your question, I am just wondering why a hollowed out trap is better than the replacement pipe MB installed for free. I don't read the MBCA list, so no idea why this is any better. SEE? NO IDEA, I DO NOT KNOW IT ALL. And I am not saying that there is NO reason this would be any better (although I sure can't think of one), just saying I don't know why it would be.
Part of my "interesting history" is that it seems like if I put the first reply in to a question, you usually get more responses added to your question, so you can take that for what it's worth.
Gilly