SandraUSA here - was looking for a solution to my smelly kitchen sink and came across this site. I noticed it around November last year. I have poured down boiling water, lemon juice, bleach, baking soda and botanic oils to try and get rid of the smell. There is a dish washer next to the sink which is used only occasionally and there does not seem to be any issues under the sink that I can see. HELP!! It is a foul smell. :(

I have a questions about this. Is your dish washer connected to your sink drain? And under your sink you will see a trap. It looks like an elbow with a bolt under it. If so open it to see if there is water in it. The elbow or trap will hold water to stop gases coming into the house. Check that and if that's not the case come back and I will give you more options. Best of luck for now.

I have checked under the sink and the small pipe from the dishwasher goes straight into the side of the sink pipe - can't see a trap it leads to a larger pipe that goes out to the drain outside.

You need a trap to prevent the gases coming into your house. That should salve the problem then.

I will get my other half to look into that and see if it sorts out the smell, thanks.