What do you do with the first infusion of an oolong
When people brew oolong, the first infusion is often discarded. It's called "rinsing the tea" by some people, and "warm-up infusion" by some other people. I prefer to call it "warm-up infusion", because I drink it up most of the time (which is not a common practice) and I don't want to feel like drinking dish-washing water :-p In addition, I believe functionally, the warm-up step is almost essential for many oolongs.
The historic root of "washing the tea" is the combination of a few factors. Many old people would say, the discarded first infusion is meant to be an oblation for the God (whatever relevant God s/he is) and ancestors. This is an important aspect of Chinese traditional life, considering tea is always an essential part of traditional ancestor worship ceremony. Another tea custom related to ancestor worship is, in Gongfu tea session, when several small tea bowls are used, it's the best to arrange them in a half circle, but never in a straight line. The reason behind this custom is, only at ancestor worship, the tea bowls are lined up in front of ancestors' memorial tablets. In other words, it's considered improper and ominous to serve a living person in the same way as serving tea to ancestors (who are dead people). On the other hand, there were numerous rules in Chinese traditional society, so many that at certain point people may get tired of them. Nowadays, many young people don't care about the old rules, or don't know them at all. Sometimes the young people may break the rules and are chided by the old guys. I do follow the "not to line up the tea bowl" rule, because you never know if a guest in front of you minds a lot about any ominous signs. But when I drink tea alone, I steal most of the first infusions which are said to belong to ancestors :-p
As a science major, I believe many cultural phenomena have physical science reasons behind them. Many oolongs, fisted or strip-shaped, are tightly rolled. And therefore it's often necessary to allow them sometime to "wake up" in hot water before they can yield full flavor. I believe that's an important reason for the "warm-up infusion". I usually use hot boiling water for the warm up, pour the water in brewing vessel, let the water submerge tea leaves, and then pour water out as soon as possible (some people would hold it longer for this infusion). Then I would spend a minute or so taking care of other things, so that the tea leaves further "wake up" in the hot vessel before the official "first infusion".
The "rinse" or "warm up" infusion also helps remove small pieces of tea debris. This can be important because many people prefer not to use a filter in their Gaiwan brewing sessions. Some oolongs, such as Wuyi, Dan Cong, many Taiwan oolongs and traditional style Tie Guan Yin, have very neat whole leaves. With these teas, after an initial rinse, there won't be much more debris coming out of later infusions.
A side benefit I've experience from drinking the warm-up infusion is, by tasting it, I get an idea how fast the tea leaves opens and release flavor. I usually use 20 sec. to 30 sec. for each of the first a few infusions in a oolong session. Some teas, such as an excellent Tie Guan Yin, can yield a sweet and fragrant warm-up infusion. Then I would use shorter time (around 20 sec.) for the next a few infusions. Many people may think it improper to drink the warm-up infusion. So I steal this infusion only when I drink alone :D
Some people believe the purpose of rinsing is to clean the tea. I generally believe tea is already one of the cleanest food stuff in our life (considering the entire procedure of sorting, pan frying, and/or roasting). In certain type of modern sanitary view, anything handled with human naked hands without gloves is thought of as "not perfectly clean". But it's not in my concern. Besides, I don't believe a short hot water flush can clean anything to much extent. If a tea is not clean enough, a rinse won't help anyway.
I've also known people who don't carry out a rinse or warm-up infusion. A Taiwan tea farmer once told me he would never rinse his tea because his tea doesn't have debris and he hates to discard any tea water. That's understandable. I often feel the tendency not to discard any tea water either. If you prefer not to have a rinse or warm-up infusion, then probably a longer initial infusion is necessary.
For a few times, I've seen people who rinse all types of tea, including green tea. Seeing green tea rinsed, makes my heart ache.
At the last, I want to address a myth. It's more than two or three times that I've read a statement that "the Chinese always rinse their tea and discard the first infusion". It's not true. I can't speak for all the Chinese, but most Chinese I know don't "always" rinse their tea, and many never rinse their tea, especially considering green tea drinkers are still the largest tea drinker group in China.