Hi Elinekl,
I did the Light to light last Xmas with my wife. We used Eden taxis, dropping my car at Green Cape and having the taxi drive us up to Boyd's Tower. The fare wasn't cheap, from memory about $180.
We did the walk over two easy days, with a camp at Hegartys Bay. I'd be reasonably comfortable with the tanks at Saltwater camp and Bittangabee Bay having water, but check with the ranger first. Last Xmas there was also good water at Hegartys Bay and Bittangabee Creek (infact I was able to have a swim there). I treated the water from the tanks with no ill effects.
I posted a trip report here
http://hiking.topicwise.com/doc/LighttoLightWalk with plenty of photos.
Its a nice easy walk with beautiful beaches and coastal scenery, unfortunately for us we got very overcast conditions so my photos weren't great.
Cheers