The Haynes manual says that I should fill the washer fluid tank up to
about one inch below the top. I did this today and was surprised to see
washer fluid running out from under the car.

Initially I figured it was due to sloppy pouring, but the leak continued
 slowly.

Looking under the car I can see the bottom of the tank and all the hoses
in the area look connected. I couldn't see it, but it felt like the leak
was coming from a crack on the back of the tank. I *could* get my hand
up there.

I also noticed that the tank seems to have a black plastic filler neck
and a white tank. Is this white tank have two parts that are molded
together and have cracked or is it likely at the junction between black
and white plastic? Should I replace or remove and try to patch it up
with something?

Thanks