Although practically all the bottle caps provided here could be used for either solvent extraction or waste collection, the difference in function lies in how ventilation is handled. 

During solvent extraction, air must enter the bottle to displace solvent removed - a problem resolved with a one-way check valve. The removeable valve is constructed of inert PTFE components with stainless spring, compatible with most laboratory solvents, with a low opening pressure below 1psi.