If it is urine, soak it in 50/50 vinegar and water. Vinegar actually neutralizes the urine at a chemical level.
If it is poo, soak it in 50/50 baking soda/ borax with warm water and EO of tea tree and lavendar to soften it up. Then scrub by hand. Then soak again for smell reduction, if it is also urine stink, soak in the above.
Then wash, after washing, smell, if stinky, soak some more.
I've had urine sit around for a long while with no horrible reprocusions. I think I've had poo too, it stained, but the smell was gone.