Re: fuel usage
Google is your friend.
You have a Universal 25, which is really a 21hp unless it's a new install after 1999.
There is a rule of thumb which is pretty simple, and accurate. Diesel's use 1 gallon per hour per 20 HP developed.
That' means at max RPM, you'll use 1 gph. Since that would blow your engine (it's not rated for continuous WOT) - call it 1/2 gallon a hour at 2500 rpm and you'll be right close.
Keeping a reasonable reserve on hand dictates never going below 1/4 tank, and carrying a 5 gallon jerry can as backup.
Lessons learned are opportunities earned.