Season 2 Ep40. When Trudy tried to kill herself she took sleeping pills from Dal's bag. Dal really beat himself up about it for days. He kept reminding himself how his parents were always so careful, always keeping medicines locked up.
So it's almost inconceivable that when KC needs something to make all the competitor's rats sleepy, so that his own rat will win the race, he finds Dal's medicine box unlocked.
Sure, KC could pick a lock, but I just don't buy that Dal would forget lessons learned when Trudy nearly died.