When I was five or so, some younger kids used to wee in a potty and pour it down a drain outside. I feared toilets (I thought they might flood, I think I used to flush and run away) and I wasn't self-conscious, so I'd sometimes wee in the drain. Someone must have had a go at my parents about it ("your son's not toilet-trained", or something) because I remember getting this huge telling off, any my parents weren't that uptight usually. and I just thought, it's a drain, if they can pour wee down it, I can wee in it. (I don't know if "if everyone did that, it would stink" would have made sense to me).
I was very well behaved for a few years, but I remember seeing a poster at a swimming pool asking people to shower, and to "use the loo not the pool", and was shocked to realise that some people would wee in the pool, showers, the bath, a quiet alley or wherever, and others thought some or all of these were disgusting, or that the only thing good enough to use was a toilet and nine litres of pure mains water.
No wonder kids get so confused.
A childhood belief about weeing and pooing

others believed things like this
- how many us believed you would go down the drain with the bath water? I did!— Amy
- I used to think that a "pool shark" was an actual shark that lived in a swimming poolAnon
- I used to think that trolls lived in my shower drain and showered with my dirty water— Troll bather
- i thought that when you were in the bath you would get sucked down the drain— blake
- I believed that the Kreepy Crawlie used to clean our pool, would follow me around the pool and eat me. — Mother-of-2
- I used to believe that once you pulled the plug in the bath a shark would swim out of the drain and eat you.— Amy