I cleaned out my sewer line inside the house, got a lot of gunk out. I thought I was done and this morning, helping around house, I was doing a wash load, took cap off open sewer line too see if it was clear-when the washer was letting water out...wam..back up again...poured harsh chemicals in line , used high pressure hose and plunger. Then I thought I'd check outside--sure enough gunk coming from outside trap....Now I think that the line is clogged from house to street...I removed concrete covering and started digging...2 feet down--water...I know there's a trap there--seen it, but I think line is clogged there.....My ques: Is there a very harse chemical I can use? I've used Nitrate Acid and that help some, but I'm sure there has to be somethingelse out there!! HELP--MAN IT STINKS!!!!