Eliminating foul odors is at the core of this incredibly potent formula. Whether the RV in question makes use of a black or grey or any other type of tank, it is just as potent. The Walex TOI-91799 Porta-Pak Holding Tank Deodorizer Drop-Ins are a one way stop to a fresh smelling septic system. This RV black tank treatment comes in little ‘paks’ which are a great avenue for portion control. Even better the enzyme formula within them is eco-friendly and just as effective as any chemical-based one. It begins work once applied and instantly begins to fight against foul odors and breaks down waste. It equally works wonders when it comes to clogs in the pipes, valves and other areas. With it’s a pleasant fresh alpine scent, it does wonders for RV holding tanks.