Turn on this hidden switch on the washing machine, all the dirty water drains out immediately

Cleaning Frequency
You should clean the washing machine dirt filter at least every 3 months to ensure that the filter stays clean.

Simple method to clean the washing machine

For modern machines, you can easily choose the self-cleaning mode of the machine. Select this mode, and the machine will automatically adjust the water quantity, temperature and time to clean the drum.

If the machine does not have this mode, choose a regular wash cycle (without putting clothes in the machine). Use commercially available drum cleaning tablets/powder or substitute with vinegar to clean the drum.
When cleaning the drum, also pay attention to the rubber seal on the washing machine door (for front-loading washing surfaces). Clean this part to make sure all the dirt is removed.