So I accidentally dropped my (electric) toothbrush into my very dirty sink (I haven’t cleaned in a very long time, but that’s another issue). Since it’s electric, the heads are expensive. What’s the best way to de-germify the bristles?
Cuppa boiling hot water. Tisp of bleach. Let it soak for 10 minutes while you clean your sink. Rinse. Brush.
Hydrogen peroxide soak.
Leave it out in bright sunshine for a few hours. But since there is zero risk that they are harboring any potentially harmful pathogens, what you need is to set your mind at ease and get past the mental yuck factor. Put a little dish soap in a pan of hot tapwater, slosh them around for a minute, rinse and air-dry. Your sink has had plenty of opportunity to kill you, and hasn’t yet.
Put some toothpaste on it and rub it against your teeth. That should clean it right up.
Clean it up well with soap and water, and then do 1 tsp / qt of cool water for 20 minutes. Rinse with clean water, and you’re good to go.
This concentration is slightly higher than the standard homebrewing bleach concentration (1 TB/gallon), but should do the trick just as well.
Winner!
Your mouth has a helluva lot more germs in it than the sink does. Nastier ones, too! Those anaerobic beasties under the gums die off outside your mouth, unless you bite someone where they can give a potentially fatal infection in their flesh.
Seriously, you’re at greater risk infection-wise from biting the inside of your own mouth than you are from using a toothbrush that fell in your own sink. Or your own toilet for that matter.
I just dip mine in Listerine.
If I leave a cover off my brush, the cat licks it clean for me…
From the sounds of it, napalm.
Not that I don’t believe you, but it seems counterintuitive; I mean, if one were to take a look at my sink in the state it’s in, and ask if it’d be a good idea to lick it, or even run your finger across it and lick that, I know what my answer would be.
It may look and taste gross and disgusting, but it’s unlikely to cause you to come down with an infection.
is it a muck out sink?
boiling water might damage.
rinse under water. dunk in antiseptic mouthwash if you want.
What’s a muck out sink? Google gave me nothing.
something like a janitorial sink in the floor. or washing muck off tools.
Use the toothbrush to clean your sink then through it away and buy a new toothbrush.
The germs that are in your sink most likely came from you, not from the tap or from the air. And even if not, if it dosn’t kill you it would just make you stronger. So go ahead and clean out the sink with your toothbrush and some hot water then brush your teeth; kill two birds with one stone. You’ll be fine. 
My degree was in microbiology. I agree with above quote.