It's hard to say, in all my years I've never heard any hard-and-fast rules or recomendations about using tea tree oil. I've usually heard numbers like 3-4 drops for use in a regular wash cycle and up to 20-30 drops for when you're looking to disinfect the diapers.

I would definetly add the oil with something else to make sure it doesn't just end up sticking to the dispenser etc before even hitting the wash water. I'd just put the drops directly on top of the detergent in the detergent dispenser. Or you could mix it with water too...

I'd just put however many diapers you washer can handle. Since you'll likely have to split up the 60 diapers I'd just go with two loads of 30...

If you have it I would run the diapers through a 'sanitary' cycle or something similar that heats up the water extra hot.

I'd also recomend getting your dd checked out both to be sure and perhaps get something to treat the yeast if that's indeed what it is.

Karen.