Prevent embarrassing rust stains and streaks with RustAid drop in tabs. Simply clean the bowl with RustAid bathroom spray gel and then use RustAid toilet drop in tabs for automatic rust stain protection for up to 45 days. Unique oxidation preventing formula stabilizes iron in bowl water to keep rust stains from forming. Safe for plumbing and septic systems. Color safe - won't harm toilet color. Safe for plumbing and septic systems. 2 tablets per pack.