The cyborg still has to break the nutrients down into forms that can be absorbed into the body. This will require not just a stomach, but some portion of intestines. These, then, will produce waste of some kind. Probably not much, relative to a typical 2,000 calorie diet of solid foods. But some.
Further, at least some liquid will need to be processed out via the kidneys and into the bladder. This will contain not just water, but the unused nutrients from the food, dead cells, and etc. This probably won't be that much different from a non-cyborg human in quantity.
The reason you didn't need to use the restroom while working in the field is that you were basically dehydrated the entire time. Not an exactly perfect environment for your cyborg.
In practice, then, your cyborg is going to need the equivalent of a colostomy bag and some sort of catheter system to handle what doesn't get digested. RoboCop could eat baby food. Which means he probably produced stuff that smelled quite similar to dirty baby diapers.
I suppose you might could drop the colostomy system if you use an IV system instead to provide nutrients. But you will still have kidneys that produce urine.
 You asked in comments:
what if the liquid food is already in a form that doesn't need to be
processed by the stomach?
The digestive system in summary:
- Mouth. Breaks food down into boluses that are swallowed into the stomach. You've removed this step entirely in your original post (OP).
- Esophagus. You are retaining this in your OP, but it's just a muscular tube that delivers food to stomach. (This also delivers air. Given how much of the face and neck you're destroying, you may need to also split this into two separate delivery tracts, just to prevent choking!)
- Stomach. This adds acid and enzymes to break down foods. Your OP posits that food entering the stomach is already at the paste-like consistency of food typically leaving the stomach. Not sure if the acids are required by your goo; probably not. Also not sure about the enzymes' necessity.
- Small Intestine. With additional enzymes from the pancreas and bile from the liver, this is where most nutrients are absorbed out of the food. Can't afford to lose this if you're using any kind of feeding tube.
- Large Intestine. Here, water is absorbed from the stool, which by the end is mostly food debris and bacteria. The bacteria synthesize various vitamins, process waster products, and protect against harmful bacteria. Again, these functions (and the bacteria behind them) are all critical if you're using a feeding tube.
- Pancreas. The pancreas is a busy little organ. It makes insulin and other hormones vital to life, but for digestion, it creates enzymes that break down protein, fat, and carbohydrates. These enzymes are going to be necessary, even in pre-processed food goo like you're suggesting.
- Liver. There are many important jobs the liver does (filtering blood for one), but for digestion, it secretes bile.
- Gallbladder. This stores bile. Bile is critical for breaking down fats.
So basically, if your feeding tube system delivers a constant, but controlled, measure of food into the intestines, the stomach can probably be bypassed.
But regardless, if food enters the digestive tract, some kind of fecal matter will emerge at the end of the process. This is unavoidable. You could build a system that collects it, dehydrates it, and mixes the water back into the food matter for reuse. This would lower the water requirements of your system. The waste would then be stored until servicing, where it would be turned over to whatever purpose (disposal, use as fertilizer, etc.).
You could probably remove the entire GI tract (but not the pancreas and liver), and use an IV-based feeding system. No food goo and no fecal matter. But even then, the kidneys will still have to remove stuff from the blood stream and that will have to exit the body as urine.
Again, you could build a urine-filtration rig to extract water from urine, and recycle that into the IV (or food goo concentrate). But regardless, the
spice, er urine, must flow.