Consider small claims since a lawyer would cost as much as repairs. Some small claims grant $5,000 in punitive damages, while others grant $7,500. Depends on the state. Do your homework, e.g., "caveat emptor real estate, bad sewer line, negligence, innocent misrepresentation." Sometimes owners and their conduits (realtors) have a responsibility to check these issues before they sell, especially if the issue emerged within, say 24 hours after the new home-buyer moved in. However, realtors are seldom held liable because they are the mouthpiece of what the owner tells them. Even so, a bad sewer line that blows out overnight for new homeowners is probably pre-existing. Take pictures of tree root invasion in the pipe, and call around to find out what works been done before. City assessors might have info, too. If the tree root invasion is massive and substantial, it's intuitively obvious it's pre-exisiting, and there'd have been backup, even for contractors say renovating the house and using the toilet part time, while the water is off the rest of the time. "It doesn't take a windmill to figure out which way the wind is blowing" -- Bob Dylan. And if the contractor is also an owner working on the house to flip it -- yet he feigns ignorance about backups -- his level of sophistication, bargaining power, and superior expertise -- in contrast to first time home-buyers -- may still make him or her liable. Lot's of case law, common law, and Supreme Court rulings (in favor of plaintiff) are all online, depending on keywords you search, & you should cite cases in your small claims petition. And former homeowners can't bring their own lawyers to small claims. They're probably already lawyered out for a civil case, and probably for good reason... but the same rules don't apply in small claims. If repair costs ultimately costs more than what small claims granted (if judge rules in your favor), you'll have a case for the civil courts after that ruling, perhaps pro bono if you still can't afford a lawyer or if costs outweigh what a civil court lawyer would charge.