Words can be just as powerful at evoking strong physical reactions as images or smells. Use your words to truly gross out a reader. You can write about an experience from your past or just create something. It just needs to be really, really disgusting.
His soft piglet flesh smelled like softness and flowers. Just like babies are supposed to. That part never changed. The taste, however, was different every time. It always depended on the age. A newborn was always the most tender and was also the sweetest. Like honey glazed ham. With every month that passed though, the meat got less and less tender. By the time they were toddlers, it almost wasn't worth the time it took to snatch them. But if they were fresh, like this one, well...his stomach was rumbling just thinking about the first bite.
The open sore on Colin's heel was giving off a strange odor. Maybe wearing his shoes without socks was a bad idea. At first he thought someone had left a jar of pickled eggs out, but the there was an added spice of bologna to the smell that made him investigate. As it was, he didn't really think to check himself until he realized the cat had been following him and nipping at his ankle, trying to lick at his foot.
I knew this one was gonna be an epic shit. I'd been fighting a case of the bubblies all day and I'd come close to unloading in my pants twice already. As it was, I'd accidentally sharted on the way in to the toilet and had to peel the drawers out of my ass crack. All was going well, until I reached up to scratch my nose and noticed the brown stain on my fingertip...
yeah, that's all I got right now.
Cypress Hill - When The Shit Goes Down