I noticed my boxer was straining and even after an extended walk nothing had moved. So I got a syringe (without a needle) and filled it with sunflower oil and squirted into his rectum. I left him for 5/10 minutes and then took him for a walk... And everything he had been holding onto came away!
I am not sure it is the right thing to do, but it certainly worked and saved me another visit to the vet. I had been giving him rabbit meat for breakfast and I suspect that might have done it.
I might try using water if it happens again. But I reckoned that a glycerine supposititory is oil... So maybe oil would work for him too!
We don't get tinned pumpkin here and we tend to only get pumpkins at Halloween. But maybe I will try the sweet potatoe someone mentioned.