Every airline is different but don't expect too much in the form of documentation. The Chinese cheat profusely on paying taxes so not much is actually paid on your behalf. I do receive a tax statement but it doesn't amount to very much which they have paid so almost basically worthless. Some airlines may pay a flat 10-15% but most do not. In other words don't count on using what they pay to offset your taxes due as it will not amount to much. This job will wear you down if you commute continually. My advice is to bite the bullet and come here for 5 years and save a bundle of cash and then move back to your home country. The schedules, long days, worlds worst ATC flow control system will eventually wear you down if you commute. I have seen many pilots come and go and those who commute generally last only 1-2 years and then quit. If you avoid the big cities in the north life is actually quite good here.