The nastiest smell I've ever encountered

On the farm there is a never ending array of foul scents that can and will assault your nose. A cow lot kinda smells, a hog lot is worse. Noxious weeds find their way into hay and can catch you by surprise with their odor. The same goes with snakes and other small animals, who weren't quick enough to get out of the way of the hay baler. When you come by a few hours later or the next day and pick up the bale it smells like dead. That's a common phrase where I come from, 'smells like dead'. No further description needed, it never really matters what's kicked it, it all smells the same. The smell of death plays a factor in this story, but scale and time augmented the odor me and my brother came across. First...

Molasses is used as a supplement for cattle and you can present it and a host of other minerals and supplements to the animals in a variety of ways. Hard little blocks they lick, lapping up small amounts of the stuff with each pass. A slightly less dry version of the little blocks which comes in what amounts to like a ten or twenty gallon little tub. Or you can opt for a liquid form that comes in a big plastic tank. The liquid tanks are pretty inventive, as they have a lick wheel. The cow licks the wheel, it turns and the sticky molasses clings to the wheel and the wheel remains covered in the stuff. That is until the tank runs empty and you have to refill it. The idea of refilling the tank is where my older brother and I come in here.

An old busted lick tank.  You can't verify this, but it's sitting in about the same spot where this little story takes place.

A guy in a truck comes by and just fills it up, but our tank had sat empty for a long time and filled up with twenty or thirty gallons of rain over a period of... I don't know how long. Well our old man tasked Jake and I with dumping the water so he could get it refilled. From a technical standpoint this is a simple task, and we set about it without knowing what we were in for. We got over to the barn lot the tank was in and popped off the top. It's like a big lid. Immediately we were staggered by the smell. There had been a little bit of the molasses mixture still in the tank when it began to fill with rain. This sweet easy to get at source of sustenance was a fly magnet. Alas flies are stupid and while they found their way into the tank easy enough a great host failed to exit. It's hard to say, but I honestly think it might have been into the tens of thousands range on how many flies made up that foul soup that rippled in the bottom of the tank.

We stepped back to compose ourselves. Jake's plan, which was a good one, was simple enough, get under one side and dump it over away from us. Side by side we grabbed the lip of the tank and hefted it up off the ground, the brown rather thick liquid pooling at the far end. It was heavier than we thought and our leverage on the tank wasn't as good as it could have been. We dropped our edge and in a rush the water rolled back to our side of the tank splashing up into our faces. I gagged, turned made it a few steps and let loose whatever was in my stomach. I was a bit preoccupied, but I think Jake managed not to throw up. The smell was... well it's hard to describe; stagnate water, pounds of dead flies, mixed with what was left of the sweet smelling molasses, all fermented nicely in the tank for weeks if not months.

It was heavier than we initially thought, but we could dump it over, we knew that much. Jake got a little angry at me cause it took me a few minutes to settle myself enough to walk up to the tank alongside him. We had stirred it all up and now the smell was constantly emanating from the mess inside. I gave up about halfway through our second attempt, which really pissed Jake off. After another few minutes of pacing around I finally walked up to the tank and we upturned the damn thing. I can still see that shit spilling out onto the ground, uhhgg.

Promptly we got back over to the house and I jumped in the shower. It's been probably damn near twenty years and there has yet to be anything I've encountered that rivals that unholy stench.