The answer to this question depends on the model you buy. Many high quality tow behind sprayers aren't actually designed with complex built-in filtration systems. They simply work by pumping the liquid out onto the lawn or surrounding plants. There are, however, some models, like the Chapin 97600, for example, which feature dual filtration systems. These models tend to have higher price tags but are able to offer more functionality and flexibility in terms of the liquids you can place into them and how you can use them.