ballast question

i setup a semi-automatic ballast but can't get the empty pump to pump at all (750 Attwood). i was wondering why can't i tee my empty back into the raw intake so w/ the motor running the pump that pumps water through the block would suck the sack down. of course a shut off valve to keep it full
please help i want to see what the wake looks like w/ the sack full but i can't fill because i can't empty it.

If your pump can push the water back into the raw water intake, it should drain w/o any issue if your atwood has a good prime. Lack of prime will cause your atwood to spin and draw nothing from the sac. However, if you're expecting the raw water intake to suck the water from your fat sac that may not work.