Flushing is mainly to remove salt buildup from the nutes that are left behind.
Also ppl flush once a month although I've heard as much as once a week.

When you do flush let the soil dry out before you water again (stick your finger in the dirt to make sure it's dry knuckle deep), and make sure to check the p
PH of the runoff water when you flush, hope you have alot or big drainage holes in those pots will help you out alot.
Overwatering is caused by frequently watering a plant not from giving it a large amount and letting it dry up on it's own.