1 cup baking soda
3/4 cup citric acid
1/4 cup cornstarch
To this add about 30 drops essential oils of your choice
I personally use essential oils that contain anti bacterial properties in them. My essential blend is:
15 drops orange essential oil
10 drops lemon essential oil
15 drops spearmint essential oil
8 drop tea tree essential oil
Whisk the oils into the dry ingredients. You will only need to use your spray bottle to mist the dry ingredients about 4 times. It will stick together when compressed in your hand. It will look very dry, yet DON'T over mist. If you do so the toilet pucks will continue to fizz and it will make a real mess.
Once you compress them into the individual molds, allow to sit for 3 or more hours to completely harden before removing them. I cover mine with a piece of cardboard or whatever I have on hand so that the essential oils do not evaporate. Pop out of the forms and store in an airtight container until ready to use. I would not suggest leaving them in your bathroom as the humidity or dampness can cause them to fizz.
Toss in one puck in the toilet and let it do its thing. Don't toss too hard or from any height or you'll get some lovely toilet water splash back into your face hahahahah! My youngest found that out the hard way. Scrub with a brush as you normally would, then flush!