Plastic pants are a cover that goes over your diaper to help prevent any leaks. They are used mostly with cloth, as those tend to bleed through more than plastic backed, but you can use them with plastic backed diapers. In that case it's used mostly to hold in the smell, or if you're worried your diaper might be full enough to leak, but you don't want to take it off. Plastic pants will a bit of the overflow, not much, but enough that you could probably get one more last use out of them.
An enema is a procedure where you fill your anus with liquid in order to induce you to void your bowels. They may not be 100% medically accurate, but in the ab/dl sense, the gist is it's a way to force or guarantee you to mess your diaper, really badly depending on the size of the enema. You can get a kit for a small one at your local drug store probably. It's like a bulb thing, looks a bit like a turkey baster. I'm sure there's a specific liquid you can use for this, but I think you can get away with just water. Fill up the bulb, lube up, stick it where the sun don't shine and squeeze. You can also get some that come in like an iv bag. You should probably look up detailed instructions on how to do that. I haven't done it myself, it seems easy enough, but it's a bit too much for me. It might be hard doing it by yourself though.
