DDog2 has the runs 
Started this morning, currently three episodes in the house and a couple outdoors, literally water now.
I think he may have thrown his breakfast up but DDog3 has probably eaten it as I found traces on the floor. Apart from that he's not been sick again.
I'm very much of the "wait and see" camp but in all my years of owning and working dogs I have never seen so much shit come out of one dog 
Apart from this he's a little subdued (hardly a wonder TBH) but is trotting round the house with the others, drinking normally and definitely interested when I was making lunch. Hasn't been in kennels recently, vaccinations up to date (we have had parvo locally so we're really hot on them) and to the best of our knowledge hasn't eaten anything grotty.
My gut says to wait and see, it's just the sheer volume that's causing me to think twice.