When I finish a wallhanging I lay it on the carpet and straighten it so it is square and I pin it to the carpet with T pins. I spray it with water so it is damp all over and then I let it dry. If it is small enough to fit on one of my foam core design board I use that instead of the floor.
Ricky Timm puts his in the washer and spins the water out and puts the quilt on the floor in the same way till it is dry. I found that my way works just as well for me and I don't have to get it quite so wet (and heavy). If you have an iron that puts out a lot of steam that sometimes works just as well.