Help! When we flush our toilet, it gurgles and backs up into the tub (raw sewage! ) It doesn't happen every time, though. We have tried plunging and pouring extra water down the toilet. Sometimes the toilet flushes with the extra water; sometimes it just fills up. We have snaked toilet and tub. Didn't solve problem. The problem is not predictable. This is a second floor bathroom, city sewer, brand new toilet, brand new plumbing. We didn't have this problem when bathroom was first redone. I am at wits end!

You have a partial blockage in your drain line downstream from the tub. Perhaps something got in there during construction. The solution would be to snake the drain. This can be done from the lavatory roof vent, the tub waste and over flow plate or you can pull the toilet and go down the closet bend. Good luck. Tom

Thank you! You were absolutely right! I had our guy come over and snake from the vent, and it seems to be working fine now. It's great to be armed with a bit of knowledge!
Take care!