Reddit reviews Sumo Skills: Instructional Guide for Competitive Sumo

I've heard people say very good things about this book: https://www.amazon.com/Sumo-Skills-Instructional-Guide-Competitive/dp/0991408608 .

Sumo Skills by Thomas Zabel is an excellent resource for Sumo training. Breaks down basic movements and techniques along with practice regimes. I've bought it and would recommend to anyone else wanting to learn Sumo.

I've been considering this one to educate myself for our podcast. Maybe you could find it useful:

https://www.amazon.com/gp/aw/d/0991408608/ref=ox_sc_saved_image_2?ie=UTF8&psc=1&smid=ATVPDKIKX0DER

https://www.amazon.com/Sumo-Skills-Instructional-Guide-Competitive/dp/0991408608/ref=pd_sim_14_1?_encoding=UTF8&pd_rd_i=0991408608&pd_rd_r=R23QWKPBR8D701V0FK2M&pd_rd_w=GkGZu&pd_rd_wg=SLQRR&psc=1&refRID=R23QWKPBR8D701V0FK2M

I came upon this while browsing Sumo. Never read it but just a thought. There's also a recommended book on that page about how to use Sumo techniques in MMA.

This book is very good:
http://www.amazon.com/gp/product/0991408608?keywords=sumo%20training&qid=1451904681&ref_=sr_1_1&sr=8-1

I know you said you were looking for something free and online, but this guide might be what you're thinking of: https://www.amazon.com/Sumo-Skills-Instructional-Guide-Competitive/dp/0991408608/