As an Aussie living and working overseas for quite some time do I still get rental income taxed? If so how much, and is there such a thing as "waiving" this tax?
Yes you still have any income derived in Australia taxed - you will have no tax free threshold, and pay 30% in every dollar of profit. (this will be determined by expenses, costs, interest payments etc - you will usually end up with not much profit.) Suggestions to reduce tax or eliminate it is to purchase a fairly new property, pay for a quantity surveyor to go through the property (about $600 - 700 dollars) to create a depreciation schedule. This is amazing how it reduces the tax for MANY years - usually pays for itself after one year.
Negative gearing is what many suggest to reduce tax - I personally prefer to make a profit, and eliminate that through depreciation schedules. a paper loss.
If the property is in NSW there is no way of reducing property tax - that is a nasty tax - but it is tax deductable in profits tax. It is also part of the reason many people in Sydney/ NSW are getting out of property as an investment option - and creating a rental squeeze.
the property will be in Thailand for investment purposes only. If I am not a resident in Australia for tax purposes, how does the rental income get assessed?
You didn't mention the property was in Thailand - I assumed the property was in Australia because your question asked about Australian Tax - the answer is NO - you will not get taxed on any profit from the property in Thailand while you are living outside of Australia. Once you are in Australia living, then it will be a different thing I believe.