One of the uses of Channel is to channel spirits. Its a basic use of the skill and essentially requires the person channeling to make a TD equal to double the APT of the spirit. Of course, the spirit can resist the Channel attack with an opposed Channel check as well. If the roll succeeds then you drain your channel skill ranks in APT away from the spirit.
You can do a couple of things with the APT you channel:
1. Absorb it.
2. Dissipate it
If you have the Medium secret or equivalent capability you can also:
3. Channel it into another person, item, etc.
Now, a couple of points. You can do multiple things and elect to absorb some and dissipate the rest. Or channel and dissipate. Or channel and absorb.
If you choose number one and absorb the APT, you are tainted by the influence of the spirit. If the spirit is a one of rage, let's say, then you can potentially become enraged, at a chance equal to the percentage of APT you drain to your own (Divide the APT your drain by your own APT to find the percent). If it was a spirit of hunger, you would be overwhelmed by an intense hunger, etc. Even if you are not fully affected, some lingering minor effect equivalent to the taint occurs. If AT ANY POINT you exceed your own APT score with absorbed APT, you become that kind of spirit, essentially destroying yourself. So, be cautious.
Now, why would you do this (absorb the spirit APT, that is) in the first place? Well, the APT you absorb heals any APT impairment 1:1 and APT damage 10:1 you may have sustained.
Now, option number two is the safest. Effectively you are draining the spirit and destroying its essence. Its the safest method.
Number three entails being able to pull energy out of a spirit and push it into something or someone else. Even if you don't absorb the energy you still feel a taint from it and suffer the minor effects.
Taint gained through absorption lasts for a number of hours equal to the amount of APT absorbed. When you channel it into something the taint lasts for one minute equal to the amount of APT moved. If in combination, add the two together.