There are slow-acting laxatives that you have to drink a lot of and tastes wile but is soft on the intestines, and then there is quick-acting laxative that is easier to get down. The former tends to be prescribed by default, obviously.

If you have no prior intestinal diseases and are in for a routine check, ask for the quick-acting one. You will have to drink the same total amount of liquid, but at least most of it will not be drinks of your choosing.

Also get anal cream, and apply it once before going to the toilet.