Hi KazB
I walked the Basin to Heaton Gap last week - over three days. Five days for you plan would be good -- possible todo in 4 if in a hurry - but it is a hilly section of the GNW with some over grown sections.
Water tank at the Basin and at Watagan HQ where both empty.
there was water in creeks (needing treating) at The Basin, Wollombi Brook, Watagan Creek (in farm), in the Crawford Tank beside the hut, some very gross looking water in the dam at the 'Saddle Rest area' west of Barrabba, Hunter lookout tank had water, Wallis Creek, Heaton lookout, some gross water in dam beside Heaton Communications tower and then a tap at heaton gap.
Take your time around the gullies through Wallis Creek area - these are overgrown at the moment and the track is not always really obvious.
hope that helps.
Happy walking
Matt