Priming methods for diesel engines vary all over the place. I'm not familiar with the Kubota engine in your Grasshopper but I can share with you the instructions in the manual for my Kubota L3000. The only difference I'm aware of is that yours has two fuel filters whereas mine has only one. See attached photo and fire away with questions.
Please note that this may or may not get your engine running. This is only the procedure for bleeding after changing the fuel filter. If the engine still won't start, you'll probably have to crack open one or more injector lines at their injectors. Just enough to let air out. Then have someone try to start the engine. After a few turns, you should see diesel fuel begin to leak at these fittings you just loosened and the engine will begin to 'hit' as it's now getting fuel. As engine speed increases, tighten these fittings. The engine should now be spinning fast enough to purge the air out of the injection system. At that point, you should be good to go.
Diesel rule #1--Don't EVER let it run out of fuel. Not only is it a PITA, the injection pump relies on diesel fuel for lubrication. Spinning it without a supply of fuel does not do it any favors.
Diesel rule #2--If you notice the engine doesn't seem to have as much power as it usually does, change the fuel filter(s).
Diesel rule #3--If your air cleaner doesn't have a restriction indicator, get one. Then, don't jack with the air filter until the restriction indicator says to, OR until a couple years have passed by. This isn't really a diesel rule but a good rule just the same. My Kubota didn't come with one but there was a boss on an air intake elbow where I suppose an optional one would go. All I had to do was drill and tap it. I used to have some diesel trucks and one of them was a 'pneumatic' truck which operated in unbelievably dirty conditions. Field reps from Donaldson and Fleetguard both said the same things--First, don't mess with an air filter until the restriction indicator says to; and second, more engines are damaged from changing air filters more frequently than they need to be. Oh, and thirdly, that the dirtiest air your engine will breathe is right after you install a new filter.
And another thing......
I had a Cat 3406B engine that would NOT start after a fuel filter change, no matter how many times you pumped the priming pump. What I had to do with it was have someone crank it while I JUDICIOUSLY squirted shots of ether into the intake. Very high risk, last-ditch method but it worked--with that engine.