You'll want to Tee in an air admittance valve after your trap under the
sink. That'll keep the 8' run of 1-1/4 from sucking your trap dry.

s


wrote in message
...
I'm installing a 4-ft. kitchenette with sink and, due to space
constraints, I am considering running 1-1/4" abs as opposed to
1-1/2" (the lines will tie into 1-1/2" about 8' downstream). What
problems might I run into wrt to draining? TIA!