Sewage back-up through the floor drain is prevented by a thing called a Back-Flow Valve. We tend to put them in when problems with the municipal lines have caused flooding in certain neighbourhoods, although some municipalities require them in all new construction. Click here for general information on basement flooding.
Back-flow dampers are not considered a standard part of all houses simply because up until now, they have been expensive to install, particularly as a retrofit. It is not really the valve that is the expense, but the fact that most back-flow valves are hanging gate valves that close the line except when water flows out of the house. This blocks any water wanting to flow in the wrong direction, but it also stops the venting function of this drain line during normal use. Since venting is required from the city lines right up to above each and every roof, the installation of a back flow valve has always required extra parallel piping that would join the city drain to your vent stack without allowing water to flow up that vent pipe. That means complications and in a retrofit, digging up a lot of concrete floor.
The Mainline Fullport Backwater Valve is build up-side-down from all others. It puts the protective valve flapper on the bottom, not hanging down from the top. This means that as long as water is not flowing in the wrong direction, it is simply a fully open drain line allowing water out and air in. It also means that a drain cleaning snake will not get caught on the gate. If water rises slowly in the line, it floats up and closes before the water reaches the height of the basement floor. If the water surges up towards your house, a special lip catches the surge and slams the door shut. It serves as a clean-out access at the same time and the model with the transparent cover allows for visual inspection without bothering anything at all.
This is one of those things that is buried beneath your basement floor that you hope you will never have the occasion to see it, let alone touch it. But this one is designed so well that it will save you a fortune in installation while being at the same time your best assurance against a sewage back-up flood. There are not a lot of us who get excited about sewage valves, but I got so excited about this one that they asked me to help them market it by working to change old habits of established plumbers. So yes, I now get paid to say good things about it but I am comfortable with that -- it is a great innovation. Click on the hot link in the paragraph above for full details.