The simple answer is no, you should not add any liquids to the HOTBIN.
As the HOTBIN is a sealed unit which achieves temperatures of 40-60°c you will find that the moisture from the waste added to the unit is retained inside the HOTBIN and may even find this as condensation inside the HOTBIN.
The compost you harvest from the HOTBIN will always contained more moisture than compost purchased from a garden centre, however this will soon dry out when added into the ground.
Adding additional liquids to the HOTBIN will cause the waste to become saturated and will result in the contents of the HOTBIN becoming anaerobic.
Is my Compost Too Dry?
Due to the water content of waste added to the HOTBIN it is extremely rare for the contents to become so dry that liquid requires adding.
If you think the contents of your HOTBIN are too dry then you can try mixing fresh waste into the dry patch and check after 48 hours, if this does not work you can add one cup (no more) of hot water (the hotter the better).
You can always check with our customer support team if you are unsure.