I have a similar issue with a smell of mildew or mould when I empty the tub. Otherwise no smell. Does this mean there is mildew in the pipes or behind the wall tiles? The bath drains slowly all the time despite using a sieve to catch hairs and using drain clearer regularly.
Thanks!

Hi Sofee and welcome to The Plumbing Page at ANHD.com. You're responding to a 5 year old dead threads so I gave you one of your own. Please check the date before you post. Thanks
Bad smells come from rotting hair mixed with grease. The solution would be to snake the drain from the over flow. (see image). Let me show you how,
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 3/3" 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. After you snake pour a few pans of boiling water down the drain along with a quart of bleach . This will loosen the grease and flush the mess out into the main. Hope this helps and good luck, Tom