I use Vanish on the longarm when I want to stabilize a quilt with stitches that I don't want to be permanent. It is a water soluble thread made by Superior Threads and I buy it on a big cone. I can spritz those stitches with water while the quilt is still on the longarm to take them out immediately and reposition the quilt if necessary. However, the thread is not completely gone until I wash the quilt. I've also used another brand (can't remember which) of water soluble thread to stabilize a quilt before quilting on the DSM, but again I washed the quilt when it was finished. I don't think you will be happy with water soluble thread unless you plan to wash the quilt thoroughly when it's done. I have tried to remove basting stitches made with regular thread under other stitches before, and it can be done but it can take a lot of time and I wouldn't intentionally set myself up to do it. I haven't used basting spray and don't know if it needs to be washed out of a quilt. I understand that you sell your quilts, and perhaps non-quilters are happier with one that hasn't been washed, but I personally would prefer to know that the quilt would survive washing without any bleeding or stitches coming out. I think most quilts are prettier after they're washed, but that is a personal preference.