Car seats are there for a lot: every traffic-induced meltdown, every spilled juice box, every road trip nap. For more, check out our guides to the Best Car Vacuums, Best Hand Vacuums, and Best Eco-Friendly Cleaning Products. “The biggest thing that I have seen when families come for a car seat check after they've washed it, especially if they bought their car seat used, is they're not assembling it correctly again,” Webb says. A car seat may look pristine and even be properly installed, but if the harness is routed wrong or the clips aren’t in place, it’s not doing its job. How to Find a Car Seat ManualBefore you even think about reaching for those cleaning supplies, break out your car seat’s manual.