When you Water Fast nothing goes in your mouth except water. Mouth was should not be used even when you are not fasting. It has so many chemicals that are directly taken in your blood stream through the capillary in your gum.
I use a tongue scraper and it helps a lot. Also gargling and swishing with warm water helps too. If you do not have a scraper then I would use a new tooth brush to clean teeth and tongue without anything on it, but water.
As for body lotion, it depends what it is made from. There are many herbal lotions available today. I usually use coconut oil, castor oil, grape seed oil and olive oil for my skin. Lotions usually kill the good bacteria on your skin. I also spray my after shave lotion on my clothes and not on my face so people around you are not offended by my Body Odor or smelly mouth.
These are parts of the fast that most of us struggle with. I would just stay focused on my goal.