Now, I'm not totally sure of the German here, but this is very possibly it; the "gun" is a tube with a trigger to shoot a jet of steam onto a fabric, garment etc., to remove spots of grease, dirt and so on, often after being treated with a solvent-type spot remover. If you want to have the German term confirmed, ask your local dry-cleaner; I know my description is right, 'cos I used to use one myself when I had such a shop.