Firefighters extinguished a small fire Tuesday night at a Winter Street warehouse for a portable-toilet rental company before it could cause significant damage, according to fire officials. Capt. Kevin Cavagnac said firefighters were called to “A Royal Flush” at 20 Winter St. at around 10 p.m. for reports of a fire. and smoke inside the building. Firefighters found a small fire inside and extinguished it. The fire had been contained by an overhead sprinkler system, but not before damaging two trucks parked inside. The building sustained minimal damage. No one was injured and the building was unoccupied at the time. The cause of the fire is under investigation.