Tig, I suppose that like putting the grey water into the tank, a lotdepends on your volumes and the nature of the drainage field. My last property before I moved to Portugal was a new build house and the drainage was perforated plastic land drainage pipe that ran for over half a mile under farmland before entering a stream. The Environmental Agency said they were happy that was far enough to pick up enough land drainage to keep the pipe clear and contain enough water that there would be no pollution. My new proposal will not be that long, but will have extra land drains connected to it.
Modern washing detergents do not contain the fat of the old fashioned soaps, and both our washing machine and drier have lint filters. For about half the year the drains will be collecting water from the land and for a few of the other months it will seep into the land through the drain perforations. It might not work for somebody who can only install a short run, or is in an arid situation.