TST™ Drop-Ins™ 1.7 oz. 15 Pieces Lavender Toilet Treatment (41559) by Camco®. The TST Lavender Holding Tank Treatment helps control unwanted odors and the liquid TST keeps sensors lubricated in your black water holding tank. The easy to use liquid, singles, and Drop-Ins contain a blend of lavender-scented surfactant oils that trap unwanted odors in your tank, making your camping experience more enjoyable. TST Lavender is RV and marine approved, non-formaldehyde and safe for all septic tanks - it's even great for portable camping toilets!