If you have a modern building, you don't need to worry about drains. If you have a very old building, believe me, you do not want to know. If it all disappears when you flush the lavatory then go and worry about something else.
As I recounted in "Roofs" above, I used to work on building sites during the Summer holidays and when I left university I had at that point spent not far off a year as a builder's labourer doing everything you can think of on a variety of building sites. From roofs down to foundations and drains.
One of the sites I worked on was in Wetherby where we lived at the time and the guy I was working with recounted how they had been called out to the public lavatory in the town centre which had stopped working. When they dug down, they discovered that the drains had never been connected. The main drainage pipe ran out of the building and just stopped. No connection. In a public lavatory used by hundreds of people every day. For twenty years.
So if you have a serious problem with your drains you need to read the above carefully and do some thinking.
Bob Cory
Modified on 31/08/2019 at 11:53:11 by ℗ Bob Cory