This is a picture of a garbage disposal
under a kitchen sink, whoever hooked this drain
line up used two traps instead of just tying
into to the trap that was already there.
Every plumbing fixture
requires a trap Hooking up two traps
like this could cause a siphon that will cause
the water to be sucked out of both traps,
allowing sewer gases to go into the home. A real
plumbing contractor would have never hooked the
garbage disposal this way.