Setting up one toilet station that stays put
In a flat, consistency of place matters even more than it does with a garden, because your puppy has no outdoor cue to fall back on. Choose a single station on a hard, washable floor, ideally just inside the front door or on a balcony if you have one that is safely enclosed, and keep it there for the whole training period. A washable pad in a low tray or a purpose-made indoor tray gives a clear edge and a distinct surface under his paws, which helps him recognise the spot by feel as well as by location.
Keep an enzymatic cleaner beside it, a small treat pot, and a lead if your station involves a trip into a shared hallway or down to a courtyard, because fumbling for supplies while a full-bladdered puppy circles is how corridor accidents happen. Block access to carpeted rooms until he is reliable, using baby gates, so early mistakes land on floors that clean completely and do not hold scent that invites a repeat.
The rhythm of the first weeks
Young puppies need the toilet station after waking, after eating, after drinking, after play, and after any excitement such as visitors arriving, and in the first weeks that can mean a trip every hour while he is awake. Overnight, plan on one or two trips as well, and take him the moment he stirs and whines rather than waiting for him to settle, because at this age stirring usually means a full bladder, not attention-seeking.
Carry him to the station if he is tiny or the route is long, since a puppy who has to walk past interesting rooms often stops halfway. Stand boringly still, use one quiet cue word, and wait. The instant he finishes, praise warmly and give the treat there at the station, not back at his bed, so the reward is welded to the place and the act.
Handling accidents without setting training back
Accidents in a small flat feel bigger than they are, and they are information, not defiance. If you catch him mid-accident, interrupt gently, carry him straight to the station, and reward any finish there. If you find it afterwards, clean it thoroughly with the enzymatic cleaner and say nothing to him at all, because a puppy cannot connect a telling-off with a puddle made twenty minutes earlier.
Track when accidents happen for a few days. A puddle ten minutes after a meal usually means your post-meal trip is too late, and repeated misses in one corner usually mean that corner still smells like a toilet to him or that he has too much unsupervised freedom. Shrink his free area, add a trip at the problem time, and the pattern normally shifts within days.
Moving toward outdoor toileting later
If your longer-term plan is outdoor toileting once vaccinations and confidence allow, start adding a lead trip outside at the easiest time of day, often first thing, while keeping the indoor station available. Gradually move more of the routine trips outside as he learns to hold on during the lift ride or stair walk, and only remove the indoor station once he has been accident-free and clearly asking at the door for a sustained stretch.
Keep the station through bad-weather days and late-night trips even after he is mostly outdoor-trained, because a flat puppy who loses his indoor option during a storm often chooses a bath mat instead. The households that log every trip, accident, and meal on KinsLe with Care Teams, marking each completed outing with its timestamp, spot the timing gaps fastest and reach a dry flat weeks sooner than households relying on memory.