I would probably find out what the dumpster's would have sold for individually, or what it would have cost to purchase replacements, and treat anything else as good will.

You should be able to make the case that the portion of the sale that's 1245 property would not exceed the replacement cost of the dumpsters, possibly even discounted some depending on condition.

On the other hand...is there any tax difference to treat it as if all you sold was the equipment? Check and see and if not, don't drive yourself crazy.

I think I have maybe filed an actual form 8594 use once or twice, but I can't actually remember when I did it.