I'll touch base on the burning and why in a second but regarding that last part funny thing just happened..

So I'm using vellejo red brown primer acrylic and I attempted to thin it with Mr Thinner and surface leveler which in a couple of YouTube videos I watched seemed to be a recommended thinker for priming Ive used it with Mr surface leveler and it works great guy when I mixed it with the vellejo primer it turned thicker rather then thinner.. lesson learned

But regarding the leveling thinner and the surfacer what are your thoughts for use? Mixing and thinning and clean up after words?

In relation to the Burning of the MEK Substitute in regards to Methyl Ethyl Ketone the Hazmat Book first responders use called the ERG emergency response guide which is put out in a combined effect by major chemical producers and the DOT sums it up as the MEK while does evaporate does so slowly in cooler temperatures and faster at higher temps, it's considered unsafe for runoff water and the vapors in high concentration unsafe for handling with out proper protective equipment like an SCBA.

By increasing evaporation you increase the Fumes and also based on concentration the flash point of the chemical so leaving larger quantities creates I higher hazard potential, if it's burned you are eliminating both the chemical in it's fluid and vapor state and in a controlled environment this is the best way to handle clean up, MEK Burns off like a fuel and at hot enough temperatures the product is burned off completely.

When you look up disposal of the product you'll find Controlled Incineration to be consider the best way of disposal.

This of course changes if we were say fighting a fire in a residence or a building where this chemical was stored and we are trying to prevent spread but overall the object in that instance is to keep the chemical cool to prevent evap and use limited water to prevent contamination then absorb the chemical with something and ship to some place that will in the end burn it off.