Howe's, available at any truck stop or store in America. Used by about every trucker on the road. I have found it much cheaper at truck dealers than truck stops, as in 21.99 at Pilot and 7.95 across the street at a Volvo/Mack dealer at the same exit. Insane what truck stops charge.
One bottle treats 320 gallons I think.
Your Espar/Webasto or whatever does NOT care, it works fine with this stuff. I've been treating all winter and running my D2 nightly and just about every other modern rig on the road does this too.
Looks like this:
https://www.walmart.com/ip/HOWES-LUB...EaAm2FEALw_wcB