Hi,

Recently when I run water down my bathroom lavoratory I hear a gurgling sound which is often (not always) accompanied by a sulfurous odor. The smell is only present when the water runs into the drain. Do I have a venting problem?

It sounds like vent problem you need to snake it from the roof and You can do the job yourself if you're handy. Rent a sewer machine,and take into the roof. Run your snake down the lavatory vent to the base and give it 20 feet more, good luck.

John

I agree with John... Also, make sure you have P-Trap installed...

Follow Johns expert advice. He nailed it! You have a blocked vent.
The noise you hear is the fixture attempting to vent through the trap and the smell is sewer gas escaping from the trap because the suction lowered the water seal.
The solution would be to snake the lavatory roof vent. Put out enbough snake to reach the base and 20 feet more. Good luck, Tom