In the middle of replacing the water pump on my 95 E320. I got a new Laso water pump and the small freeze plug that was mandatory to order also.

Question - what's the freeze plug for?

Does this go into the unused extra port on the WP?

I have an o-ring and flange cover that came with it to cover that port so it seems unnecessary to use the freeze plug. It looks like the right size for that hole. So can anyone explain this or am I missing some other place for the small freeze plug???