By which mechanism does lymph flow through lymphatic vessels.

would it be active transport, lymphatic pump, contraction of muscles, or pressure from adjacent blood vessels. I am leaning towards the latter.

Since this is not my area of expertise, I searched Google under the key words "lymph movement" to get these possible sources:

http://www.ashlandacu.com/LymphaticSystemHealing.htm
http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/420954&erFrom=7857716109074805760Guest
http://www.byregion.net/articles-healers/Exercise_Lymphatic.html

I hope this helps. Thanks for asking.