I am not sure where I read about using Elmers Washable School and not sure exactly when I decided to give it a try. But it is the most Fabulous and Valuable item I use with quilting now. First off, from my own personal experience if you buy a different washable glue, try it on fabric that you can throw away....my ironing board cover was stained and the applique I was using had to be thrown away. With Elmers I have never had any issues.
I do not use a special tip, just takes some practice and experimenting to figure out that you only need a pin sized amount spaced anywhere from half an inch to an inch apart. Each person will discover their own "comfort" zone with spacing. I like to place the glue dots right along the edge of the fabric, place my binding piece on top and line it up, then press with a hot, dry iron for a few seconds. Moving on down the material. You can also just let it dry naturally, but that takes to long for me. LOL.
I also like to use it for applique. I like to use starch for turning under the seams and then place a few dots of glue onto the applique back seam, lay it in place and then use the iron and press till dry. If it is not where you really want it, either spritz with water or just gently pry it apart. So much simpler than using pins!!!
With basting, I like to do half and half. Get your backing laid out just like for thread basting, lay your batting on top and smooth everything flat. Then I take and fold the batting downward about half way and just start placing a small dot of glue every place you would normally pin or take a basting stitch. Again, just a small amount of glue is needed. Then, I like to gently go over pressing to dry the glue with an iron, but I have also just let it dry naturally. After your backing fabric and batting are dry. Then I do the top the same way. Some people apply the glue to the batting also. Either way works.
The main key is to remember it only takes a tiny amount of glue. Once you are finished stitching, quilting it will wash away in the washing machine.