Won't suck the water from overflow

[illusive38]

I have an '87 mk3 turbo with a new (As of January) Japan-amoter. I recently was having over heating probs and blew the radiator. (A crack in the fill spout.) So I put on a new brass, all metal, radiator and water pump. The problem now is that it won't return the water to the radiator from the overflow. So I am still losing water.
I noticed extreme amounts of Leak seal in the last radiator. I attempted to flush the engine prior to replacement. There seams to be no clog in the return lines and I can blow the water back into the radiator when applying pressure backwards through the overflow. (With my mouth) The pressure is strong when hot and no leaks are apparent. I find no oil in the water or water in the oil. The cap that came with the radiator is a 16 pounder. The car exceeds stock specs for speed and power, 0-60 etc....so I know the motor is strong. The turbo is up to about 12psi. Everything is strong.
Frankly, I'm stumped. I just want it reliable so I can get on with more speed, power and handling related issues.
Oh, and the water light is continuously on.