Well I'm certainly no expert but there are biodegradable soaps that you can use. We use them at our place. There is a soap named "Camp Soap" that is biodegradable and we use the
Dr. Bronner products.
There is a debate as to whether or not biodegradable products are good for the environment or not but I'm not getting embroiled in that discussion.
He could also place a filtration system on the exiting grey water if he was really concerned about it.
