An apparatus and method are provided for preventing or reducing buildup of certain solids in a system or a conduit containing or conveying a fluid. The fluid can be a single phase liquid, such as a liquid hydrocarbon, or a multiphase fluid such as a mixture of several immiscible liquids, for example liquid hydrocarbon and water, plus a gaseous phase that may include hydrocarbon vapors as well as other gases, for example carbon dioxide, hydrogen sulfide, etc. Preferably, the fluid is crude oil. The solids include all solids precipitating from fluids due to thermodynamically or chemical composition driven forces, as well as materials that can change phases. Preferably, the solids are solids typically dissolved in crude oil, such as higher paraffins, asphaltenes, hydrates, organic salts, and inorganic salts. The method involves passing the fluid through a treatment apparatus placed before the system or conduit under conditions sufficient to deposit the solids within the apparatus, slurrying the solids, and passing the resulting slurry to the system or conduit. The apparatus includes a passage having a length sufficient to effect substantially complete deposition of the solids.