It’s the same here by code grey water (laundry, kitchen, showers, etc) have to go thru the same tank with the solid waste. I feel a certain amount of fluid flow is a good thing anyway with helping the solids break down. In my old house the plumbing went back 100 years, and it was set up with laundry and kitchen going directly to what they call a grease trap just before the leach field, kind of a small septic tank about 100 gal. the solid waste went to the septic tanks (3) 300 gallon tanks in a row and then on to the grease trap. This IMO was a great setup the shower water combined with the solids seemed to break down well and all that laundry soap gunk and kitchen gunk was caught by the grease trap. Every few years I would have all 4 tanks pumped at once and the leach field always stayed nice and clean.
The new codes wont however allow it done like that. But I suspect many people still divert the wash water to the leach field on their own at some point. I don’t like the idea of those soaps going straight to the leach field however. The addition of a grease trap is a good idea. The way mine worked is the tank I used was fairly tall and the exit pipe had a tee that had a drop pipe to the center of the height. Anything that entered the tank that would float stayed in the tank and anything that would sink sank to the bottom. I also had a screen right before the output line that I could check from the open top of the tee.
I was able to rebuild mine as it was grandfathered in at the time I did it and it was just a week before the new unified code took place. I took that window of opportunity to build a new grease trap and replaced the leach line I had with something more like a mound system. Keeping the water and leach lines close to the surface rather than deep how it was done in the old days.