FWIW, I think you may have been given some advice that confuses a couple of processes.
Most 3D printers use isopropyl alcohol to wash the excess printing resin off of the items before they are post-cured in UV light. (There is also a class of 3D printer resins that are water washable, but I suspect that’s not what you’re dealing with, here.)
The lines that you’re referring to are often called “layer lines,” and they are artifacts created by the limited printing resolution of some machines. Angled surfaces and compound curves are subject to a “stepping” effect as the printer finishes one layer and then stacks the next on top of it. What can be the visible result are lines formed by the edges of the layers.
Some newer printers and updated software use features called “anti-aliasing” to essentially print an extra “half layer” around the edges of each normal layer, but the best cure is to print with higher resolutions (thinner layers with less visible lines around them) or to use true SLA laser printers (that expose and cure the layers one voxel (think 3D “pixel”) at a time.
However, for items that have already been printed, and that have visible layer lines, there’s no “un-ringing that bell.” The only cure is to either physically blend the lines by sanding or filing, or to fill the lines by applying a heavy primer paint (or some combination of both).
Consider: If you were able to “wash away” the layer lines by submerging in acetone, you would also wash away all of the similar resolution details on the model (edges of buttons, belts, insignia, etc., etc.). This is also one of the problems with trying to fill the lines with heavy paints or primers - what fills the layer lines also muddies the desired details unless the filler is carefully brushed on just in the places it is needed.
The bottom line is that there are no shortcuts, just lots of a new kind of parts prep. Instead of removing mold seam lines, injector pin marks, filling seams, etc., you’re now carefully sanding, scraping and filling layer lines.
Not all 3D prints are made equal, so informed purchasing is the order of the day (and one reason why good reviews of 3D models, parts and figures should have macro images of the surfaces).