Why does a single unit cost almost as much as two?

A single unit costs almost as much as two because the truck trip and driver's time are the biggest parts of the fixed cost, and adding a second unit doesn't double them.

The delivery fee covers the fuel, driver labor, and truck wear for the round trip from the yard to your site. This cost is the same whether the truck carries one unit or its full capacity. The service visit fee works the same way; a driver in a vacuum truck spends the same travel and setup time to pump one unit or several in the same cluster. The rental rate for the units themselves is the only part that increases directly with the count, but it's a smaller portion of the total quote.

For your wedding with 140 guests over six hours with alcohol, the units per person guideline suggests more than one standard unit. A single unit would likely be overwhelmed, leading to long lines and a full holding tank. The quote structure makes adding a second unit a cost-effective way to improve guest comfort without a significant price jump.