A "tip" - is a landfill (hence a mother may say to her child "your room is a tip"

"Tipping" is (among other things) the act of dumping trash (probably comes from the tipping of a wheel barrow
and/or a dump truck...but that's just a guess)
Hence you may see signs on certain areas of land saying "No tipping" (which is kind of a redundant sign as its
patently obvious that its not cool to just dump your trash anywhere)

"Fly-tipping" is basically just "tipping on the fly". ie. dumping your stuff then making a getaway.

Why does this happen?
The local services often refuse to take certain items (such as televisions, sofas, carpets, mattresses).
But many people are fundamentally opposed to paying to have something taken away, going on the belief that
this should be a free service covered by the taxes they pay.
So instead of paying for removal they just a take a drive late at night. Some are insidious and drive to a quiet piece of
unused land...some are more brazen and just dump the stuff on the pavement (sidewalk).

-Mike