Seller did not disclose plumbing problem; what is procedure for having seller pay for repairs?

Question Details:

After a week in our newly purchased house, a waste water backup resulted in our having a camera sent through a discharge pipe. The plumbers identified a significant hole that has existed for a while.They also see that this pipe has had a plumbing cable sent through before to clear the line. The seller answered "no"on the SPDS disclosure form with regards to existing plumbing problems. How do we proceed in having the seller pay for what will be very significant repairs? Important Notice