I wouldn't recommend using soap on your rectum - it can irritate. Just wipe with paper, then rinse bottom with water from a bottle; dab with tissue to dry, then wash your hands with soap. That way I never get skid
After defecating and customary wipe, wash area with soap and water. Do a full squat and insert your soapy middle finger into the anus once or twice to push anal canal residue back into the rectum. Hygiene is IMPORTANT, no sharp fingernails and thoroughly wash afterwards. This procedure has NEVER failed since its discovery to prevent underpants stains. Hygienic
Well, yes... If you don't quite feel completely "fresh" (ie, there is poop in between your rectum and your outer butt), you could always insert two squares of tissue, folded, in your ***-crack, OR you could poop, wait a bit, then SHOWER before bed.
As for your "being poor and eating a lot of beans and rice", eating beans and rice might be cheap, but it's also an extremely good diet to have - lots of protein and lots of fibre! (I'd be concerned far more if your diet consisted mostly of "hamburgers and white bread" which is almost like BEGGING to have colon cancer.)
I used to have the same problem, I managed to tackle it by changing the way I wipe because I found that I was never completedly clean. Now I just wipe as usual until I am as clean as I can get then I use a travel toothbrush to buff the area. When your done you just rinse it off and put it back in your pocket so you can take it anywhere you go.
I'd be sure to drink a glass of water about two hours before bedtime and then poop right before going to bed, in hopes of clearing the passage until morning.