it's different with everyone...you will figure it out on your own. and if you had a bad experience with one type of food, be sure to try it again at a later date. things change. fish used to make my output pure liquid, now not so much. as was mentioned you can eat stool thickening foods as well if you notice that you have a particular issue wuith a certain kind of food. ie if you're having problems with fish, serve it with potatos and you might be fine.
as for speed, i notice whole proteins (meat) take the longest for me to digest. so if i know i'm going out for the evening, i'll eat just meat for supper. veggies go through me really fast, so i tend not to eat them. i take a supplement instead. there is something to be said about volume as well-eat physically more and you'll have more output. eat physically less but with the same energy (calorie) value, and you'll have to empty your bag less, but still meet your nutritional requirements.
hernias...i've never had one, and have done quite a bit of lifting. i go to the gym daily and do situps/legups/leg press etc etc without any problems.
--matt