If you are having problems with liquid output the first thing to try is loperamide with your doctors approval. You can also thicken output with dietary changes such as peeled apples and apple sauce, marshmallows, bananas, rice, pasta and noodles, smooth peanut butter, sago and tapioca, white bread and plain biscuits/crackers, jelly products.
Basically any soluble fibre will help as it absorbs liquid. Google soluble fibre to find choices that agree with you remembering that for 6-8 weeks post surgery you need to be careful about what you eat so you don't cause blockages.
Metamucil or benefibre are made from soluble fibre so can help - sounds counter intuitive I know since they help constipation, but the hospital put me on to them.
And yes I can hear everyone laughing since despite the above advice and following it I still have liquid output. I'm beginning to think its all the tea I drink - its got to come out somewhere but its so much more pleasant than water, or worse, the sweet salty water I am supposed to drink!