I know what you're talking about with the decaying smell. It's truly horrible. I had to do a necropsy on a dog that had been dead for about two days, then spent some time in the trunk of a car on a hot day, and I almost barfed! The people in the waiting room of the clinic complained about the smell too, it was that powerful.
The worst smelling thing I ever smelled was a dead zebra we did a necropsy on in my fourth year of vet school. They had treated it with DMSO, which is an IV drug that smells like mashed up onions and garlic, left out to rot for a month. It's really foul smelling stuff. Now, add a rotten onion/garlic smell to the smell of dead animal. Blech!
You smell a lot of horrible things working in the medical industry.