The most common place is right at the outlet. If it was properly
installed the smallest opening and sharpest turn in the whole system will be
at the outlet.
First find out what outlet(s) have low suction. That should direct you
to where you need to look. As noted a light weight plumbers snake can be
used, but be sure you don't poke it into the motor unit. :-)
I suspect you will find the problem at one of the outlets and if you
look carefully you may see some sort of string snagged there and the clog
will be on the other end of that string.
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