Additives for Grey Water Holding Tank

Agree as stated above. No need for chemicals in the gray tank. Dishwashing soap and shower soap will keep the tank pretty clean. If you want to give it a good "swish" cleaning, drain the tank, pour some bleach down your drains, ad a few gallons of water and just drive around. The bleach will clean the tank just fine. Be sure to drain the bleach water (catch it in a bucket and pour the bucket down the sink or toilet in your hosue) and then add some clean water to rinse the slide valve off. You don't want bleach only sitting on the slide. Rinsing by adding more water will keep it from drying out. No need for tank additive chemicals. You've already got everything you need.