Because your two drains "tee" into each other right under the sink and go
into a single trap. Proper kitchen sink plumbing has two traps, each
dumping into a vertical pipe of the next larger size.
<atcctl> wrote in message
I can see a potential problem. I have a double sink and use one trap. The
trap, however, is lower than what your is coming from the disposal. You can
pump water literally right across the tee and up the other drain line. Mine
on the right goes straight down to the trap, the one on the left comes out
of the disposal and goes straight down, then over to the trap.
In spite of what one poser said about the need for two traps, my single trap
has worked perfectly for the past 27 years.
The problem is that the disposer thrusts out waste material with
sufficient force that it doesn't fall down the "T" immediately --
instead it gets thrown into the other sink. A better solution would be
to use an "L" from the disposer output to send the stuff straight down
to the trap. In the vertical run to the trap you may be able to use a
"T" for the second sink drain. The combination of gravity and no bend
from the disposer reduces the likelihood of waste backing up into the
other sink. However, it appears that the drain line to the wall is too
high to accommodate the "T," so double traps may be the only solution.
Just have the disposer output take a straight shot to the wall.
the real solution is two traps with two drain lines combining several
feet below sink level.
had this problem with my old house, in prep for sale it was a must fix
plumber did this one, and when we re do the kitchen here i will do
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