Synonyms for Wash down:

n.

glug, choke down, gorge, down, gulp, guzzle, chug, drink to, force down. rinse, wash off, scrub, swab, hose down, swill, flush out, mop, wash, Disinfect. wash down (noun)
flush down.

v.

drink (verb)
down, guzzle, swill, gulp.

Other synonyms:

drink
gulp.
Other relevant words:
guzzle, drink to, swill.