I did this about a year ago and I've been pleased as punch with the results. Took me a while to learn enough about plumbing to make it work, but that was because I was starting from ground zero. Anyone even a little plumbing savvy will have no trouble with it.
Here's the thread, complete with proof of how ignorant I was at the start, along with completed pics of the result.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29231505.cfmIf you're camping with hookups, this is absolutely the way to go. TP consumption drops significantly and the whole thing is just much cleaner and more pleasant. The smaller RV bowl will fill a bit, so sometimes as you use it you might want to step on the pedal to drain the bowl.
This is probably less than ideal for boondockers or those who aren't setup to drain the black tank easily as you will put more water in there, but the reduction in TP and the additional water will keep your tank cleaner.
To answer the question of where the water goes, the bidets commonly sold for easy home use are actually attachments for your normal toilet. They have a sprayer that does the dirty work and the water just drops into the bowl.