It's been so long since I did any "serious" modeling that I don't remember the answer to this question so checking in... Is it a required step to wash 3D-printed building kits with soap and water before painting? I don't know what "format" it is, just that it's gray plastic. I figure it can't hurt so I was planning to do it anyway... unless there is a reason I shouldn't. The specific building in question is the N Scale version of the "Christmas Story House" which I picked up via that Well Known Internet Auction Community last year.
If it's resin printed them yes you need a wash. Many have used Bestine, denatured alcohol, etc. to remove the wax coating. If it's filament printed then you don't need to but I would do a surface wipe with alcohol anyway.
I use Simple Green cleaning solution diluted 50-50 with water. An overnight soaking removes wax coating.
depends on what type of printer it was made on [resin or filament] ... if you are not sure a bit of a wash in bestine or alcohol would work okay for both types
Since you are not sure what method was used for the printing, I'd say go with the denatured alcohol was just to be safe.