Camco TST Ultra-Concentrated Orange Citrus Scent RV Toilet Treatment Drop-Ins, Formaldehyde Free, Breaks Down Waste And Tissue, Septic Tank Safe, 15-Pack (41189) Eliminates odors and helps break down waste in the RV holding tank Ultra-Concentrated: just one drop-in treats up to a 40 gallon tank Does not contain the toxic, formaldehyde-releasing ingredient bronopol RV and marine approved; Safe for all septic tanks Fresh citrus scent, 15 drop-ins/bag