Thanks for the links but I do not buy them. Like I said in post #13, I know for a fact that the pressure in the below slab pipe in a basement flooded with 12" of water is exactly the same as a stand pipe with 12" of water. Theses folks are stating their opinion, as we are, but they are totally wrong and they are not stating a fact.

Zgeist,
So whadda you going to end up doing? Inquiring minds want to know. Tom

Well, I'm probably going to put in one of those flood guards for a little peace of mind. And that may be all I end up doing - but I'd really like to have a check valve installed on the main line, too. But that may never happen unless I feel flush with cash. ;)

Where does your sewer enter the house? How deep is it? If you're able to do the digging we can walk you through installing a sewer check valve. Tom