Oh lucky you! We had slugs in our first flat (basement) and first house (both damp and rented). First step is to figure out how they're getting in and block it. Ours appeared to be coming in under the back kitchen door, so we added weather stripping to block all the visible gaps? we also wondered whether they'd crawled up the drains - mesh covers outside might help if you suspect that. But then we discovered they were breeding under the cooker. Putting slug pellets under all the appliances seemed to do the job - obviously the pellets need to be kept out of reach of any children/pets as they are toxic. If you go down to the affected room in the middle of the night and suddenly turn the lights on you may get a shock/figure out where they're coming from. Also try tracing the slime trails. Ghastly things. Good luck.