Ooooh, poor Rumor, poor Gene!
It could be so many things. And often you can't find out from a stool sample unless you are lucky when you get the sample.
(I use a plastic spoon to get the liquid kind, just so you know...)
When my pups have had that, I treat first for worms, then coccidia (any time they have been exposed, you get that in your yard and you always have a new bout of it sometime).
For worms, you can buy Safeguard (for cattle) online, the liquid kind only...and give it to him (and the others because they pass it back and forth) at 1 cc per 4 lbs of weight.
For coccidia, you need to give Albon. You can get that from the vet (of course they will want to see Rumor and won't give it unless he tests for it.)
One time I had a whole litter that had very explosive poop...no tests were helpful, the pups' temp was high and I had one very lethargic pup. I took that one in to the vet who confirmed that "something" was going on...and assumed that a good antibiotic would help. He gave us enough for the entire litter, it was Clavamox. Well, it cured them all.
I know that many people like holistic methods and to work with foods...and I agree...but when they are really sick, I combine the two. I give antibiotics or dewormer AND a bland diet...and, of course, lots of liquids.
Good luck!