Treat the stained areas with baking soda paste? Spread it on, let it dry, and scrub it off.

using an old mug or buy one of these foldable silicone sterilising cups: http://www.femininewear.co.uk/foldable-silicone-sterilising-cup-3442-p.asp pour boiling water from the kettle over your cup and leave or heat in the microwave when relatives are out.

or you could buy some Milton tablets here: http://www.femininewear.co.uk/milton-sterilising-tablets---box-of-28-4839-p.asp and use one with the cup/mug to clean your cup with.

you could also soak a cotton wool ball in rubbing alcohol and wipe it over the cup briefly or the bicarb paste as suggested above scrubbed with an old toothbrush.

to prevent stains make sure you're rinsing the cup with cold water after emptying (hot water cooks the stains on, similar to only rinsing/scrubbing blood stains from bedding/underwear with cold water) and use a mild soap to wash after each emptying if at home, morning and evening if not.

Edited at 2013-10-11 07:28 am (UTC)

I normally use Milton tablets for cleaning but I haven't felt they've been very effective with stain removal. I second bicarbonate of soda though, I scrub it on with a toothbrush and it's a faff but really helps!

I use denture cleaning tablets. I can't guarantee that this is safe, and there are a thousand different kinds/brands. But it's a fact that my Fleurcup always comes out looking like new.

It's very unlikely to damage the silicone in any way, but there might be a residue that may or may not be vag-friendly. Use at your own risk.

This. Tried and true!
Peroxide is freakin' magical on blood stains (on anything).

I do about half and half. Or a 1/3 peroxide and the rest water. Looks like new the next day. Or after work :p. I do it every 3-4 months.

You're in the US, right? Plain ol' hydrogen peroxide, straight out of the bottle. No diluting necessary. Let your cup soak overnight in a small glass, then rinse it off in the morning. As others have said, silicone can withstand much stronger concentrations of peroxide than what we get in the first aid aisle. And it's not a very stable liquid. Just like soda loses its fizz, the peroxide will have become yucky tasting water by morning so you can't "oversoak" your cup. Cheap, readily available, easy. If you want to dedicate a special glass, then pick one up at a thrift store or yard sale.

I'll add my vote for the peroxide too. I claimed an old coffee mug that won't ever see coffee again just for this, lol. My diva stains terribly towards the end, no matter if I'm washing it with cold water and soap or just a quick rinse and swipe with tissue. It seems the brown sludge yuck that I have to deal with after the first two terrible heavy days causes the stain, I don't see it until then. An overnight soak gets rid of it all.

Another container suggestion: I use an old chewing gum container (you know, the ones that fit in car cup holders) to soak my cups in hydrogen peroxide solution. The good thing is that you can close them, and the size is perfect.

I use peroxide too - a couple hours sitting in it, and my cup looks brand new. (And this is for really set-in stains; I only soak it about once a year.)