How should I include third-party models in my domain model?

Question

I'm currently trying to design a little application using Domain Driven Design but I'm afraid I don't really get the concept yet. Let me try to explain this as clearly as possible.

public interface IMyDomainRepository
{
    void Add(IAnInterfaceFromAThirdParty element);
}

The interface above is defined in my domain model and this will be used in a different project called ThirdPartyImplementionVersionX.

Now IAnInterfaceFromAThirdParty is not defined in my domain model but comes from my third party library.

I could create a class/interface in my domain model which implements the same properties and methods as the interface IAnInterfaceFromAThirdParty but this interface has 20 methods defined thus making it a difficult task to implement the same logic.

Is this the way to go or am I missing something?