Must be shipped to a physical address. We will not ship to P.O. boxes. The very 1st dye in a direct inject product Dye Inject is the concentrated version of Enviro-Safe Dye VS. Fully compatible with mineral, ester, and Pag oils Uses a precisely selected, florescent-yellow dye that is highly visible and is the same dye used by auto makers in car A/Cs This product performs best in heat pumps, split and mini- split units, packaged units, microchannel coils, coolers, and commercial units. Applications: heat pumps, split systems & mini split units, packaged units, and microchannel coils DO NOT use in ammonia systems One-time use Concentrated No need to pump-down R410 or other units No injection-hose or caulk-gun needed Concentrated formula means less material in the system