I clean my snakes water dishes every few days, they get fresh water almost daily(please don't kill me, there are some days I'm legit not home except to sleep) but if the bowl is soiled I immediately wash it in the kitchen sink, usually just with Dawn in the kitchen sink and completely towel-dry before placing back in the enclosure.
If I'm just doing a water replacement I fill from the bathroom sink, its convenient. What I actually do is have a small pouring cup[ that I fill and use to fill both dishes, I have a hard time putting full water dishes into the enclosure without making a mess so its easier to fill the dish when its already in there.
I would say using whatever sink you want is fine, provided said clean dish isn't coming in contact with other possible contaminants. The only thing I can see if your roommates somehow being grossed out that you equate your pet's dishes to a humans by washing it in any sink .. lolwot.
tl:dr, you're fine, use whatever sink is convenient.
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