Calling is the quickest route to a price. Say what the system is doing, the tank size if you know it, where the tank sits and how a truck can get near it, and the crew gives you a number and a time. The number said on the phone is the number on the invoice unless the job changes when the lid comes off.
If a call is not convenient, send the form with your address and a line or two about the problem, and you get a call back the same day. A photo of the yard where the tank is helps.
For a backup into the house, an overflowing tank or an alarm, call rather than write. Those go to the front of the day.