I would reccomend that you epoxy the inside surface of the tank. Then bleach the heck out of it. By the time the chlorine taste goes away, you''ll be happy with the flavor. Don''t run a heavily chlorinated solution thru your water pump. It has a tendency to eat rubber.
The product of choice IMO to build fiberglass water tanks is WEST System. And the Gougeon Bros have done all KINDS of testing with their products, and are eager to share the results with potential customers. If their book is not available to you, I''d enourage you to call them (see product literature for a phone number) and discuss what they think.
I would expect WEST system epoxy to instill no foul taste to the water, but better that you hear it from them...