Washing should be enough. Make sure that you don't dry the cover and padding. And NEVER machine wash the straps or completely immerse them in water. They are spot clean only. I wouldn't want Lysol on something my child was going to be that close to every day, especially their face. Line dry it in the sun. If you think it smells funky, mix some white vinegar with warm water and spray it. Vinegar is a cure-all - cleans and deoderizes as well as repelling pests, all naturally without chemicals that baby or other people can inhale.
Since its a used seat, also run it through this checklist
Its actually unsafe to get a used car seat unless it is coming from a trusted friend or relative and you are 100% positive:
1)it has never been in any wreck
2)it has all the original pieces, including manual
3)it has never been dropped, which means never been checked as luggage at the airport, either, since this frequently happens when checked or gate checked .
4)it is less than 6 years old
5)the straps have never been completely submerged or washed with anything other than mild soap(it messes up the flame retardent treatment)