Tell us about yourself!
just a little cat common knowledge: MINT IS NOT A DETERRENT. In fact Catnip, is a plant common to the Mint Family and known to produce the same effects on cats that are exposed. In short, Cats LOVE minty smells and HATE SPICY odors like Citrus peels, pepper etc.(https://www.smartlivingnetwork.com/cat-breeds/b/feline-101-cat-safe-grass-and-herb-gardens-for-spoiled-happy-indoor-felines/) Here are effective natural cat repellants: http://m.wikihow.com/Make-Homemade-Cat-Repellent
Septic tanks RELY on bacteria to biodegrade the effluent(solids in waste water etc.) recycled back into the ground and require monthly dosages of these bacteria (Sold as Rid-X and others) into the system to keep it working efficiently and not backing up into the house. Spitting mouthwash or any other cleaners/antiseptics (hence the term, eh?)into sinks, toilets WILL damage a septic tank after if done for an extended period. For more info on how septic tanks work see here: http://www.sunplumbing.com/how-do-septic-systems-work/ or video https://www.youtube.com/watch?v=uuORuwb4cfs