What does the cryptic crossword clue "Glass tubes broken up for starters, one of us getting knocked over (8)" mean?

The wordplay uses acrostic. BU (synonym="BU") + SETTER (reversal="SETTER") = BURETTES The answer is BURETTES.

Glass tubes broken up for starters, one of us getting knocked over (8)

Guardian Cryptic #26511 | 17 Down | 2015-03-05 flower