I signed up for a machine quilting class on Craftsy and the instructor (Ann L. Peterson) demonstrates how she spray bastes. She uses either Sullivan's or the 505 spray and emphasized two things:
1. Spray very very lightly. She says that she never gets gummy needles.
2. Spray the wrong side of the quilt top and the wrong side of the backing rather than spraying the batting. Spraying the batting soaks up too much of the spray which can lead to the gumminess and also wastes spray.
In the video she sprays outside on her patio table (covered with a clean dropcloth) and she does spray VERY lightly. Then, back inside, she straightens out the sprayed top and backing and then layers it with the batting. She demonstrates how re-positionable it is.
One step she says is important is to press the sandwich after layering it....says this really sets the glue. She pressed the backing first then only minimally pressed the top. In her quilting demonstrations she really handles that sandwich and it stays together quite well.
As for the Craftsy class...I'm enjoying it and learning lots. It's much longer (hours) than I anticipated and she is a good instructor.
AnitaSt