I used a naptha-based grain filler on my ES-3, and it did take the water-based stain I used. But I did try it out on some scrap wood first. But not all grain fillers are the same, so I do strongly suggest testing whatever filler you decide to use on another piece of wood first and then staining that to see if it takes. If you can get hold of some Timbermate, then I'd use that in preference to anything else.