well the shtf | Page 3 | The Compost Bin | Forums

damn that really sucks, you need to keep a lateral plug on hand if you can't get that backflow preventer installed.

are you in a low lying area? if the main is 8" then it needs at least .4%. they may have laid it flat.

a lateral plug works the simplest way possible, just like a valve but you'll have to get your hands dirty shoving it in the pipe (probably 4"). it plugs the line going to your house. so either you could plug it at the manhole (if your lateral goes directly to the manhole) or you'll have to plug it at your cleanout, which could be difficult if you only have a 4-6" stand pipe, it'll be hard to fit. plus you have to be around and aware that it's about to overflow, at least it would give you the option to stop the flow even after it has started. better to have the sewer overflow out of the manhole and into the street than out of the lateral and into the house.

but if your finished floor is below the rim of the manhole you may have a recurring problem on your hands. I'd go open up the closest manhole, see if you can see your lateral dumping into it or not, see if your manhole is at the end of the line or does it have more homes connected upstream?.

See how deep the manhole is from rim to invert, then measure the distance to the next manhole, open that up and see how deep it is. if it's almost the same depth then you've got a flat sewer problem, gravity sewer needs a certain slope to keep the sewage velocity enough so it doesn't back up. If it's flat then you are going to have a recurring problem. It's really your towns responsibility, but if it's a small town you'll sooner be elected president than get them to spend the amount of money it would take to fix it.

I also saw you mentioned a restaurant, this could definitely be the source of your problem, if they are connected downstream of you there is a large possibility that the grease they dump down the drain is causing your back up.

roots blocking a main is a usual cause, how old is your neighborhood? they can clean the sewer but if roots really are the problem it won't truly be fixed until they replace the sewer entirely or slipline it. often times when they clean old sewer it will make the holes created by the roots worse.