A huge, buttfuckload of shit. Like a guy just shat out Oprah and Cristi Ally at the same time. Usually smells bad enough to kill a small animal, it will plug the toilet and sometimes fill the septic tank. Plumbers will forever hate the person that made the Mefac, cursing them out as the walk out of the bathroom in a tattered has-mat suit.
" I plugged the toilet!"
"Mefac bad, oh God 3 rats just died on the floor"
"I'll get the gas masks"