It will be located close the inside portion of your water heater. You might have to remove a cabinet panel, lift up a dinette seat, or something like that to get to it. I am not sure specifically where it is on a 26tbss.
Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS