You have to think of Soylent like you would any other meal. What you've essentially done, is binge eat.
Say you took 2500 calories (or whatever your daily amount is) of traditional food (maybe 3 big macs, 2 large fries) and ate it all within 20 minutes, would you be hungry afterwards? Certainly not for a while. But if you did that at 10 in the morning, would you still feel satiated at 8 PM? My bet is on "no", because that's not how hunger, insulin levels, etc. work.
Regarding the bathroom situation, same thing. If you eat that many calories of food at once, you're probably going to have discomfort, no matter what type of food it is.