as much or as little, but you may need to do it a few times. I'm not sure exactly but once the the xylene looks cleaner I stop. So essentially you should put one part water to one part dirty xylene and shake, let settle, take the bottom layer(water) out and dispose, do this 4-5 times.
You can make syrian rue tea by grinding up the seeds and boiling them for a little, that is the fastest most effective way.
If your making ayahuasca then you should probably mix the seeds and MHRB together in water, 3-5gs of seeds to 10gs of bark. lower the ph to 5 or something using lemons or vit. c. crushed. I'm not certain so do some research, that's what SWIM did when SWIM tried it.
PEACE