I'm a DIy'er and planning to install one of these later this summer.
If you go to the Toto web site http://www.totousa.com/ProductDetail.aspx?ProductId=729
They have the engineering drawings and installation pdf's.
It states: For vertical drain installation, drill a 3-3/4” hole on the subfloor 3-1/2” from the front of studs.
For left or right drain connection, it is recommended to install the drain at 45º or more from the outlet horizontal.