Simple process to open the access hatch, remove the 5 bolts and put a measuring stick down to the bottom. Way more difficult to find the parts that drop into the tank during this process - ask me how I spent this past Saturday, ask me how a 25" flexible claw device from HD saved me big time...
Anyways, just replaced mine yesterday with a Moeller from HC. really easy to do. The one I bought ranged from 6 - 24" and you snip the sender to fit.