Why is there a thin strip of plastic or foam like material in the window washer resevoir? It seems to be loose inside the tank. What is it and what is the function of this?

 

when the float hits the top 'crossbars' the reservoir is full.
If you fill it up all the way, the fluid will leak out where the fillerneck and reservoir meet.
I can't tell you how many customers bought those cars new and brought them back to us at the dealer complaining of 'packing material' in the washer tube.
I still see them where people havecut out the plastic crossbarsto pull the float out.
Ahhhh those were the days