I heard that tubs have more ability to "push" water since they hold a mass.
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Which is more "lore".
Where are the facts?
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Any shower drain can be made with a 1.5" opening, and anyone can glue a reducer into a 2" opening, so the fixture itself takes a 1.5" drain.
When all is said and done, I find the 2" diameter requirement for showers to be overkill.
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I'm surprised that after many years of searching, I've never seen an internet comment from an experienced Master Plumber telling me how Code changed over the years.
I'm 100% certain that a 1.5" drain line used to be Code everywhere, for showers. I'd like to know what discussion went into voting for the new size, 2" diameter.
In Canada a 1.5" drain line is still permissible for a shower. Everyone says so, but I've never seen it in writing.
Having said all this, of course, do not decrease any drain line in the direction of flow. The trap size has to be the same as the drain size. Many people conclude that a 2" trap can be reduced to a 1.5." pipe after the trap. Use a 1.5" trap if the drain line is to going to be 1.5" diameter.
I'm not a plumber. Since this is a discussion forum, I'm posting this here as part of a *discussion*; I feel that this forum is the right place for this discussion.
Code has changed over the years and will continue to change in the future.
I'd like to think I'm helping to air out the issues which leads later to clearing up confusion about 2" shower drains.
Imagine all the people who have been forced to do a lot of extra work for no reason !! When a 1.5" drain already plumbed could have been used, they ripped it all out and put a 2" drain in.
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