Why are the toilets on the train connected directly to the tracks?

If you’ve ever used a train toilet and had a sudden, uncomfortable realization about where everything goes, you’re not alone.Waste Management

For decades, passengers around the world have asked the same question—sometimes jokingly, sometimes in genuine disbelief:

Why are train toilets connected directly to the tracks?

It sounds unhygienic.
It feels outdated.
And once you know, it’s hard to unknow.