Adrian wrote:

Mizter T ) gurgled happily, sounding much like they
were saying :

If you check the floor, you'll see holes that allow water (or
other liquids) to drain out.

Now I presume people at night have a tendancy to throw up, or
urinate on the bus, hence the plastic seats and the drains. Or,
perhaps it is so the bus company can literally jet wash them in
the depot. Or, both!

Said drainholes also exist on many other models of buses that don't
have any plastic seats.

Could, perhaps, be something to do with lots of people getting on
with soaking wet shoes and umbrellas which promptly start dripping
everywhere...?

I don't think so. I've only ever noticed said plastic seats on a few
London Central Bus Co buses, and they're only ever on the last three
rows on the top deck. Wet shoes, wet umbrellas and wet clothes don't
restrict themselves to that part of the bus.

I was thinking more of the drain holes in the floor...

Aha, now I understand your comments! Yes, IMO the drian holes are a
sensible addtion to bus design - for the reason you state; for draining
away any spilt liquid courtesy of an uncourteous passenger; and to
drain away excess water used when cleaning/mopping the floor. I reckon
the last reason is why they've appeared.