We do gas and electric water heaters for lots of residential customers. I have found asking the customer to send a couple of photos of their connections and heater set up before we go out saves time. This way we are sure we have the specific or special fittings for water lines, gas fittings or vent pipes for gas units. We carry most items needed, but several times we ended up needing something. This makes the installation and turnaround time go quicker.