some advice if you want large, uncontrollable messes:
buy psyllium husk, the substance varies from brand to brand. this post mostly regards the finely ground powder stuff. some others are not ground into a powder, in which case it contains less fiber per volume.
take about 0.5 DL (0.2 us cups), and mix it with water, stirring vigorously, make sure there are no dry lumps in it, untill it forms into a porridge-like consistency.
you eat this throughout the day, not all at once as that will be too uncomfortable. just eat like a spoonfull every half hour or so. drink atleast one to two liters of water during.
beside the psyllium, which gives an unnatural texture, i like to eat either beans or lentils to supplement. like two or three servings with mainly legumes through out the day. you could make falafel wraps or whatever you like.
your sleep will probably be restless, but by the morning, if you are regular like that, and drink coffee and so on, you wont be able to hold it in.
this works for me, but bodies react differently.