Yesterday I heard gurgling in the toilet when the shower was on and when the bathroom sink was draining. I did a load of wash this morning and now the toilet bowl is not draing and water is backing up into the bathtub. The bathroom sink still drains. Can this be fixed with drain cleaner or should I skip that step and call a plumber?

While your tub is backed up, run water in the sink and see if the water level rises in the tub. Sounds like you need to call a plumber and have your sewer augered. Or you can do it yourself. Just rent a power auger ( the big one) and either go in from a cleanout, minimum size three inch, or pull a toilet and auger from there. But I do recommend a pro. They will make it a much quicker job, and if they are true pros, they will clean up the mess afterwords. It can be a messy job.

Never mind, thanks. I have my answer.

Just out of curiosity, what was the answer?

My question was whether drain cleaners might work or whether I should just call a plumber.

I'm not going down the drain cleaner route, and have instead purchased a plumber's snake and am using it on the air vent. It's dark now, so will have another go at it in the morning.

If still no luck, will call a pro.

Thanks for your response! I hope the solution stops short of messing with the sewer, but at least I'm aware that might be a necessary.

I'm not going down the drain cleaner route, and have instead purchased a plumber's snake and am using it on the air vent. It's dark now, so will have another go at it in the morning. Good choice! In my opinion snaking is the only sure way to clear a clog. But before you go up on the roof to snake the vent try this. Snake the tub from the overflow plate first,(see image). Unscrew and remove the overflow plate,(The one with the drain lever) and pull out the tub stopper. You now have a clear shot at the trap. The way you were going in through the drain it ran you square into a tee that you can't get around. Now feed the cable( 1/4" best or 3/8" with a small tip. You can rent a Ridgid K50 sink cable.) About 2' down you will run into the bend of the trap. Crank and push at the same time to work around it. Your blockage will be found in the lateral pipe going to the stack. You shouldn't have to put out more then 10 or 12 feet. I have found tub and shower clogs to be mostly hair and the worm should auger into it and pull it back. Hope this helps and thank you for rating my reply. TOM