The landlady is an aged old lady in a home somewhere, who is under legal guardianship of a friend who doesn't get a penny of our rent. I don't think it is a scam, it's an ancient farmhouse in the south of France where no one has bothered to do anything about this because until now there was no one using a washing machine or dishwasher so the issue didn't really cross anyone's mind, I suspect. Not sure she pays the wastewater portion of any bills, I think they're included in our water bills. I'll see if I can get the ball rolling for the house to be connected to the sewage system, but in the meantime I want to minimise the damage I cause.
I would inform your water company and possibly the environment agency. The only water that can be run off into a soakaway is rainwater.
I assume your landlord is getting a reduction on the wastewater portion of his bill by using a septic tank. And then getting good value from that tank by only filling it with wastewater from the toilet!
I discovered yesterday that the waste water from the kitchen (i.e. sink & dishwasher) and the washing machine in the house we are currently renting, goes into a hole in the ground below our garden. Not into the septic tank, just into a hole.
I am going to buy the most biodegradable washing up, cleaning and laundry products I can. Are there any other issues I need to be aware of? (We're renting till next summer, I can't see the agency installing a new system, though I could be wrong).