i am installing a standpipe in the laundry room for the washing machine drain. because of space considerations i would like to use 1 1/2" id pvc which will run in the wall and will tie into the larger main pvc drain after about a 12' run. does anyone know of any pitfalls to watch out for in doing this. i know the height has to be higher then the tub and the slope has to be sufficient for good drainage. thanks!