Section P2706 of the International Residential Code:

Under water receptors it mentions that standpipes shall be a minimum 18" and a maximum 42". What part of the plumbing is this referring to?

Laundry tray connection: It mentions that standpipe for clothes washer shall not be less than 30" and the laundry tray connection shall be a maximum horizontal distance of 30" from the standpipe trap.

Is this referring to the pipe from the laundry tray to the ground? Or from the tray to the main sewer drain?

Section P2706 of the International Residential Code:

Under water receptors it mentions that standpipes shall be a minimum 18" and a maximum 42". What part of the plumbing is this referring to?
this is speaking of the pipe you use to connect the drain hose of your washing machine.

Laundry tray connection: It mentions that standpipe for clothes washer shall not be less than 30" and the laundry tray connection shall be a maximum horizontal distance of 30" from the standpipe trap.

Is this referring to the pipe from the laundry tray to the ground? Or from the tray to the main sewer drain?
It is referring to the tee or other fitting used on the horizontal line.