I meant the Clothes Washer drainpipe trap.
In the US generally the standpipe trap for a washing machine must be above the floor, but Canada generally allows standpipe traps to be above or below the floor from what I think I remember reading.
I have a correction to what I wrote.
http://www.co.lincoln.wa.us/Assessor/Building/Top 10 plumbing mistakes handout-4-09.pdf says
No standpipe receptor for any clothes washer shall extend more than thirty (30) inches, nor less than eighteen (18) inches above its trap. No trap for any clothes washer standpipe receptor shall be installed below the floor, but shall be roughed in not less than six (6) inches and not more than eighteen (18) inches above the floor.
I know the rules vary from place to place in the US.