Bathtub vent before or after p-trap

[bigboxer]

I am putting in a new bathtub, the old install had no vent. I am 75" from main 4" stack. Can I use a wye to tie in the new vent to drain line? If so where does it go before or after the p-trap..? Nothing else is on this drain line just the tub.

[hj]

If it was before the trap, it would not only not protect the trap from loss of seal, but would give sewer gases a direct access into the bathroom. It goes between the trap and the drain line connection.