Well... after reading https://what-if.xkcd.com/35/ What if 35 on the xkcd website I became amazed by Operation plumbob (http://en.wikipedia.org/wiki/Operation_Plumbbob#Propulsion_of_steel_plate_cap) and want to recreate potato canon style! I will use a penny as the manhole cover and a pvc pipe as the tunnel. So... any recommendations as fuel or pvc thickness or anything else?