K,
older housing the rain water goes down the drain to the sewage works, our 1980s house does this.
Modern houses the rainwater has to go to a soakaway and not into the sewage.
I'm not sure when the change was made and it is not retrospective, thank goodness.
Peter
On really old houses, depending on the underlying geology everything goes to soakaway apart from the soil pipes. Our cottage (pre 1600) originally had just a privy in the back garden which had a gravity drop to a brick septic tank. Somebody installed indoor plumbing I would guess in the early part of the last century and routed some of the other waste water into the tank, but our scullery sinks still drain to soakaways and that's in the new build half of the cottage (1865). Fortunately Cotswold limestone is great at draining so we've never had a problem getting rid of water.
