My washer and dryer is upstairs along the hallway in a laundry closet. My
Drain line from the washer runs down through the walls to the drain under
The house. My problem is, there is a leak somewhere in the drain between
The second and first floor in the walls and its coming out on the sill under the house.
I would like to know how to replace that drain line without tearing my walls or floors up?
Please help. Thanking you in advance.

If your walls are that wet inside they must be opened anyway and the drywall replaced. Hard to repair or replace a drain pipe inside an existing wall cavity.