"Installing one on your main sewer drain could just be an invitation for creating a clog at that point—uneven surfaces within the line acting as a catch point for …ummm…toilet paper."
Up here in Canada, there’s been a love/hate relationship with the BWV. The 1995 National Plumbing Code in Section 4.6.4 - PROTECTION FROM BACKFLOW states: (1) “A backwater valve or gate valve shall not be installed in a building drain or a building sewer.” (See appendix A)
Apendix A 4.6.4(1) says: The installation of a backwater valve or a gate valve in a building drain or a building sewer may have proven acceptable on the basis of past performance in some localities and their acceptance under Article 1.4.3 of this code may be warranted.
The first revision of the code in 1996-7 states in 4.6.4(2) “A backwater valve may be installed in a building drain provided that it is a “normally open” design conforming to… and does not serve more than 1 dwelling unit”
The plumbing field is one that I have not worked in (except for my own work; have Municipal Plumbing Inspectors Course for HI interests) so lack a little experience in the trenches. But the only time I saw a blockage causesd by a BWV was in a 2 month old house built by a contractor and plumbed by who else…his brother, the plumber! He did not have enough grade on the building drain and a tampon first caught and then other stuff…the house was rented to college students.
I have a line in my report (my own report format) regarding BWV’s. If I cannot find one in the basement, I refer the client to my appendix in which I tell the client to call the local authority to see if surcharge from the street sewers has been a problem in that part of town. If they can’t get an answer, canvas the neighbours and if anyone has had an incident with surcharge from the street, install a BWV.
I have seen too much of this. A friend of mine had an incident about 8-9 years ago resulting from a heavy summer t’storm… came home to 5’ of crap in his basement from a combined municipal drainage system. He had a small basement but it was loaded with art, 52" TV, $$$ stereo, family heirlooms…in all, it was a $60,000 cleanup!