Not knowing the offer/inspection contingency terms, would generally seem that if you don't want the property due to these items, it would be time to give the seller a notice of defects you object to and if they have a right to cure in the WI Offer, they can agree to fix those items before closing and move along or tell you they won't fix them and the deal is dead (or if they weren't given the right to cure defects, the deal would be dead) but again, would need your agent knowing the terms to discuss with you or an attorney or advice from both. If you have time on your inspection deadline you can also throw out an Amendment to the Offer giving other options for the seller to consider (seller credit, lower price, more time for further repair bids, etc) if you do want the property if these items are addressed (also assuming the seller didn't disclose any of these items to you, although an old roof is usually pretty obvious and just worked into the offer price up front).
It is confusing for a plumber to offer no repair solution (is it a broken sewer main outside of the house that company doesn't deal with, etc) so sounds like that may need more getting looked into. If other items drain though, it seems the washer may just be broken and the toilet a stand alone issue?