How do sweet deals from sites like DontPayFull work? On-site, we have a set of oils & fluids coupon codes, oils & fluids promotional codes and oils & fluids discount codes. For the oils & fluids offers and extra products, you can get corresponding coupon codes as well. When you visit the online shopping site where you are making a order from, all you have to do is key in the coupon code. It works pretty much the same practice that an current magazine or newspaper coupon does. Once the code is applied, you can get a certain proportion off the original price - which means big savings for your online shopping purchases!