where are you washing all this grease off to?
MY BAD! IMHO, all of us are responsible for the way WE impact the environment. Not preachin', just sayin'.
I hope to pressure wash the rear end and frame without any special fuss about the waste water. It's mostly road grime there.
The engine is another story. What I'll probably do is pull the motor and strap it down good onto my small trailer. It has a mesh floor. I can then haul it off to a place where I can catch and treat the waste water. That would have the least impact on the environment and won't kill the grass in my own back yard.