There isn't. That's the whole point. Killing or destroying the bodies with chemicals or gas gets ludicrously expensive and exponentially more difficult as you add more bodies to the pile. The "best" way to do this is the way the Soviets managed it: either shoot all the dissidents or create a man-made famine and starve them all to death, then chuck them into a mass grave somewhere and fill it in. That's it. That's your "best" and "most efficient" way. Bullets or starvation and then a mass grave.
This is the single biggest reason the Holocaust cannot possibly have happened, and it's the one thing the Holocaust asserters can never provide an answer to. There simply is no way of killing that many people and leaving no footprint or paper trail or remains. You CANNOT just 'disappear' that many corpses, it simply cannot be done. You can vanish one person like that, sure, or even a few dozen. Serial killers and organized crime managed it all the time and still manage it today. But tens of thousands, hundreds of thousands, millions? Absolutely not.
They show you a giant pile of shoes in Holocaust museums because a giant pile of ratty old shoes is all they've got. There are fields in Eastern Europe where human teeth still float to the surface during heavy rains because of all the mass graves beneath them. Where are all the Jew teeth? Where are all the remains?
Beyond the logistics of the fuel and industry you would actually need to cremate this many people, beyond the physical realities and limitations of cremation itself, there simply is no answer to your question, and that's the biggest proof of all that the Holocaust did not happen.
130,000 people died of Typhus in labor camps due to allied bombing cutting off the supplies for the German hospitals that were keeping them alive. Anything beyond that is Jewish fairy tales.
