What does it mean if the smell still remains after unclogging a bathroom sink?

I would first run some hot water, then fill the sink with hot water and bleach. Then once it’s full, unplug it and let it drain. This should help clean off any extra stinky sludge that is stuck to the pipes where you couldn’t reach. If it’s not completely gone then the problem may be deeper. Also, run your dishwasher empty with some bleach in it. Sometimes the smell is stuck in the drain from the dishwasher and that is the nasty smell you were originally getting. Especially if you rarely run your dishwasher. If you have a split sink it could also be from the side that has the disposal. Do the same there as I said for the sink. Garbage disposal get very stinky as well.
If none of that works then call a plumber.

What you cleaned was the pee trap, that u shaped pipe is supposed to have water sitting in it to stop sewer smelles from coming up, quick cheap fast fixie pour a few cups of cold coffee down the drain it will kill the smell fast.

Oh, I’m sorry. I didn’t realize you said bathrooms sink. Never mind the garbage disposal and dishwasher. Just do the bleach with water treatment. If it’s still clogged and draining poorly then run a drain snake through it before the bleach treatment. If you live in an apartment then just call the maintenance man because the problem may be actually coming from your sewage system.

Put about 3 tablespoons of baking soda down the drain. Slowly pour about 1 cup of vinegar behind the baking soda. Wait 10–15 minutes and pour some hot water ( I heat mine in the microwave) down the drain. Wait maybe 10 more minutes to turn on your hot water tap. Let that hot water run to finish flushing out the pipe. The baking soda neutralizes any odors and the foaming reaction of the baking soda and vinegar helps clear any gunk from the pipe. It doesn’t matter if you use apple cider vinegar (brown) or distilled vinegar (white) as they work equally as well. Since I first tried this, I only need to repeat maybe once per year. I do this with all my sinks and even the bath tub.

Make sure the vent trap has water in it. That’s the U shaped part of the pipe under the sink. That water serves to keep sewer gas from venting into your house.

@Blackwater_Park That is what I said ,just using coffee in the trap takes the smell away fast.

Run some hot water and put a little baking soda and some vinegar.