2005 SANTE Centre Ballast Tank Q's

[GAGS]

Hey Guys,
Our 05 SANTE is much slower to fill the belly ballast than the port & starboard. This is more noticable when underway. I am aware of this models fill pump issues and the fact that the centre tanks water inlet does not feature a scoop but the huge time lag has me guessing.
Before I start ripping the pump to bits & checking the helm valves can anyone make a few suggestions?
Thanks.

[DanielC]

Check the simple stuff first.

Is the through hull pick up clear of debris? Are any hoses kinked? Is there something in the pump impeller? Is the vent on the tank clear?