I can only tell you what I do that has worked for me going on two years. everyone's body is different. before my first use every cycle i wash it with my dr bromner's soap. i generally only change it when i'm at home so at changings i just rinse with warm water after i dump etc. then at the end of each cycle I let sit in a cup with hydrogen peroxide. so far so good:)

I only sterilize between cycles too (either boiling, or dropping it into a cup of water with a Milton tablet). When emptying, I rinse it out with plain water and re-insert.

I boil the cup before every cycle. During the cycle, I just rinse it with plain water. (If available. In public restrooms I use toilet paper, but I find water much more convenient.)

I sterilize my cup after ever period using Milton's sterilising tablets (the dissolvable tablets that are used for babies bottles - a pack of thirty will last me for years and years cos I use a quarter tablet per period). You could also just boil your cup in a pot of boiling water for at least ten minutes, either just after or just before your period. During my period I rinse my cup at each change (approximately twice a day) with soap and water (if I'm at work I will use the antibacaterial soap) - but again, this will depend on if you can access soap and water discretely (my work place has antibacterial soap and water available in each stall). Even rinsing with clean water will help - I know many women will take a drink bottle of clean water with them to help with rinsing. I think it's a case of figuring out what works for you and your circumstances. Just remember (sorry to be crude) but a normal, healthy woman can expect non-sterilised items (such as the male equivalent parts) to be inserted into their vaginas - cleanliness is necessary and awesome, but complete sterilisation is not needed.

Sterilize? No need. Nothing else you put in there will be sterile. "As clean as cutlery" is good enough. How clean does a spoon have to be before you put it into your mouth? Similarly, while hygiene is important, how clean are your partner's fingers, tongue, penis, etc?

If there is a sink handy, I like to give my cup a quick rinse between insertions. If not, that's fine too. The few drops that remain won't make any difference. TP tends to stick so I usually don't try to wipe it. Between cycles, soap and water disinfects and sanitizes almost as well as boiling -- so why risk damage? Chemicals? All I do is soak it in peroxide once or twice a year to clobber dingy-ness. But that's to make it LOOK nicer, not make it "cleaner."