If you press this hidden switch on the washing machine, all the dirty water drains out immediately

Cleaning Frequency
To ensure that the filter remains clean, you should clean the washing machine dirt filter at least every 3 months.

Easy method to clean the washing machine

For modern machines, you can easily choose the self-cleaning mode. Select this mode and the machine will automatically adjust the amount of water, temperature, and drum cleaning time.
If the machine doesn't have this mode, choose a regular wash cycle (without putting clothes in the machine). To clean the drum, use commercial drum cleaning tablets/powders or replace them with vinegar.
When cleaning the drum, also pay attention to the rubber seal on the washing machine door (for front-loading surfaces). Clean this part to ensure all dirt is removed.