I see an awful lot of people just dump it on top of the ground. I believe the local Health Dept frowns on that. The second popular option is to have a separate disposal system for the grey water, as some of the others have mentioned. I believe you will find that the Health Dept will approve it if they believe it is safe and adequate.

Some friends of ours built such a secondary field using a couple of lengths of "Infiltrator", which is a hard plastic material used for leach fields. Each piece is about the size of a coffin lid and similarly shaped (rectangular, domed down the middle). The advantage to the infiltrator is you can dig it up when it plugs and either move it over, or just hose it off and re-cover it. They used the same material for their septic drainfield, and in the 10 years since the system has been operating, they have had to move the laundry field once, but not the septic field.

Steve