Container that held soap for a carwash = food-safe?
 

Would you consider that food-safe or no? (the container would be used for holding rain water/tap water)

PEHD, LDPE and HDPE plastics are inert to detergents and soaps and as such are pretty safe to reuse. PETE is also safe, as long as there is no BPA residue from the manufacturing process.

Rinse them several times in HOT water before use and they will be fine. ;)