Finally starting on the heater install and have a question on where to install the "hot" hose. I have a sensor on the top where Al installed his so am thinking the location Jester shows in the pics here would make the most sense.

https://forum.moomba.com/showthread.php?9877-Winterization-Procedure-with-pics-by-Al&p=82556#post82556

The problem is that the bolt at that location has a square head and nothing in my tool box fits it. I thought just a 3/8" extension would work but it's a little too big. Ideas? Maybe they did that so guys like me don't remove it?