Trying to fill my washer fluid and the 1qt concentrate went right in but it seems there is something like vapor lock going on because when I add water some goes in then the neck fills up and it won't take any more.. weird huh?

 

Yeah that sounds odd.
The only time it comes up the filler pipe is if the tank is full and starts backing right up. That's how I know when Ive put enough washer fluid in when I can see it coming up the filler pipe. Although I premix mine before topping up, that shouldn't make any difference.