You've probably heard of this natural method of disinfecting diapers. This is obviously one more misinformation about cloth diapers.
Here's what's going on:
The sanitize properties of Tea Tree Oil (TTO) and Grapefruit Seed Extract (GSE) are totally ineffective in laundry situations.
To have a real sanitize action on the laundry, you would have to put so much essential oil, that it would be extremely toxic.
It would take about 30 ml of Grapefruit Seed Extract per 3.7 litres of water to sanitize and 150 ml of Tea Tree Oil for 3.7 litres of water to sanitize.
Considering that a wash cycle uses about 60 liters of water depending on the models and the chosen cycle, one would have to use about 500 ml of Grapefruit Seed Extract and about 2500 ml of Tea Tree Oil per wash, to have a real sanitizing property. In addition, essential oils are not miscible in water, they need a dispersant to dilute in a water base.
If you like the smell, you can put a few drops in your laundry tray, but this will be its only use, perfume slightly.