Tarros is more easily approached from the Dunphy Camping Area in the Megalong Valley, than it is from Katoomba. There are quite a few options for loop walks from the Dunphy Camping Area, including:
Tarros Ladder/Duncans Pass
Tarros Ladder/Carlon Head
Tarros Ladder/Dunphys Pass
Tarros Ladder/Harmil Ledge
The routes are all described in the notes below - you can put the various bits together yourself:
Tarros Ladder and Carlon Head - Bushwalking NSW
http://ozultimate.com/bushwalking/walk.php?nid=732Dunphys Pass and Harmil Ledge - Bushwalking NSW
http://ozultimate.com/bushwalking/walk.php?nid=792Duincans Pass is the easiest return route as there is little exposure. The track may be a little hard to find. The spikes on Carlon Head (Mansons Ladders) are not in good condition, and in fact several have broken off in recent years, so the going is very exposed and potentially dangerous. You could alternatively use Dunphys Pass or Harmil Ledge as the other half of your route - Dunphys is probably easier going up, while Harmil Ledge is probably easier going down.