How low can a trap be below the bathtub drain. I was told it had to be above 12".

Hi Ron:

The maximum TAILPIECE out of a PTRAP in my area is 24". That being said, you can have a piece of pipe as long as about 20-24 inches maximum from the trap out to the fixture. The shorter the better, however, as increased vertical distance can increase the chance of the trap getting siphoned and allowing sewer gasses to escape into the home.

Let me know if you want to discuss...

MARK