OK, so the pump wasn't working at all so I decided to take it out to inspect it which was the reason for starting this thread in the first place.
First thing I noticed were the feed lines were full of sludgy crap, so I bench tested the pump just in case that was all that was wrong - no such luck. Inspected the rubber bellows that 'powers' the pump in case it was cracked and leaking air, but it was fine.
Seeing as the lines were all gummed up I figured the pump internals may be as well, so I started pulling the pump apart. Bellows came off easy enough, then I was left with a flat disc with a hole in the centre on the top side and the chamber with the inlet and outlet pipes on the bottom. Saw some pics on the web that indicated these two parts just screw together and after much cursing was able to get them undone:
The bottom chamber was badly gunked up to the point where the simple ball & cage check valves in the inlet and outlet pipes could no longer open and close:
First thought was to submerge the part in CLR but that didn't do much. Then had the bright idea of immersing it in a solution of Draino and after a couple of cycles - success!
Put everything back together with plenty of plumber's lube and now she squirts like a beauty. Thanks for all for the suggestions and advice and I hope this may help someone else down the track.
