I'm assuming the dog has ascites, fluid in the abdomenal cavity, which could be caused by liver failure. It's not in the stomach but the abdomenal space. When i worked at the vet yrs ago, we'd have dogs with ascites, vet would clean their abdomen, stand them up, (if they could or would stand) and stick a big bore(16 ga needle) in the abdomen and drain the fluid. Would make the dog more comfortable and would relieve the fluid for a good while. I guess now vets no longer do that.
I know as of about 4 yrs ago they were still doing that procedure. I assisted in one. Depending on the dog, they stay relieved for a few weeks, but some fill back up pretty quick. Worth a shot though for sure.