Unless you can use around 500mL or .15 of a US Gallon to wash dishes by hand, use your dishwasher (thats with a full dishwasher, 50 pieces and using 30L of water).
If your septic system is old, and the pipes are collapsing, as is happening to a close relative's home, then you may not wish to use the dishwasher, unless it drains straight into the sink, and isn't fighting against some blockage (their DishDrawer is un-used due to this - the sink takes around 5 minutes to drain, and ends up draining through the inspection point and rusted air-vent!)