Floor Drain Backflow preventer question

[chopper72]

They make the backflow preventers to fit 3 inch and 4 inch pipes. I have a concrete opening to the drain that is about 3.5 inches.
I was wondering if I could buy a core bit for my hammer drill and enlarge the opening to 4 inches? Any other ideas? I live in a city with poor sewer capacity so when we get heavy rains the sewer flows back into the house.

Thanks!

 

[Hyper48fan]

What you call a "back flow preventer" is actually called a back water valve (FYI). The bits you're looking for are called "SDS Core Bits", do a Google search and you'll find them. I don't recommend them if you are going through a think wall. The hardest thing to do is get proper slope/grade through the wall.

 

[Joe]

I had the same problem: looking for a 3.5 inch backflow preventer when the only ones available is either 3 or 4 inches in diameter. I solved the problem by cutting a small section of abs plastic pipe with an external diameter of 3.5 inches and an internal diameter of 3.0 inches. This section of piping fits tightly into the 3.5 inch drain opening and a 3 inch backflow preventer would sit nicely inside the abs plastic ring. There is no need to change the diameter of your drain opening.