Canned pumpkin

I'd start with a whooping tablespoon or so.  Sorry, that's the way I cook too....a little of this, a little of that.......you an always increase it if that isn't enough.  It sure isn't going to hurt him any.

 daily? or per meal?

 depending on how loose the stool is I would put it in one meal and see that works - if it doesn't do the trick for the poops i would add it to each meal - as Glenda said it certainly won't hurt - I have given it to my boy as a veggie for several meals and not had any adverse reactions

 My vet said I can give my 25lb girl up to a 1/4 cup of canned pumpkin per day to help with digestive and anal gland issues, so I'm sure that amount would be fine for a bigger dog for sure, though I'd split it across his meals so he gets good tummy coverage throughout the day.

I give my two 65lb dogs approximately 1 tablespoon per meal.  I don't measure I just plop a spoonful in the food. 

Oh, I'm glad that I'm not the only one who "plops"!

Yes, I would use it every meal for a few days just to give things a chance to equalize in the digestive tract.

I never plop.

I have, however, on occasion, been known to eyeball, smidge, and drizzle.   

 It sounds suspiciously like giardia.  Try a round of Safeguard - you can get it from any pet supply place, no prescription needed.  It's packets you sprinkle on food (wet food is best to ensure a full dose, poor baby will have to eat some canned food, lol!).  You treat for three days in a row, then it's best to do it again in about a week.

 I've tried pumpkin worse during poop issues and it did nothing, possibly made it worse, lol.

 i'm getting some mixed results with the pumpkin ...

 I used it with Sandy for a bit and it took about 3 - 4 days to see results. I fed it to her until the can was gone and she got a tablespoon each meal.

It may take a little while to see results from the pumpkin.  It may also take a 2nd round with the Panacur even with negative stool results.  Giardia and the other can be difficult to catch on stool screens.  A while back both Woobs and Indie had the runnies and it took 2 doses of Panacur to get Indie back to normal.  Woobie gets runny from pumpkin at first.  It took 2 weeks of him being on it in his homecooked diet before his stools adjusted.  It could also be the food.  The only 2 things that Woobie has done well on has been Hill's z/d and this homecooked formula I had developed by a nutritionist.  It could be your dog will do best with very few simple ingredients.  An elimination diet may be in order to truly track down what's upsetting him.  Good luck!