It becomes difficult to remove stains over time, but by using warm water of about 45 degrees Celsius and leaving it in the water for a long time, the effectiveness of removing stains will increase.
(Please note that if you leave it on for more than 12 hours, there is a possibility of re-contamination.)
Also, if it doesn't come off the first time, if you soak it several times, the dirt will gradually come off, so please try it if you like.