How can I repair a pinhole leak in a washing machine drain hose?
For a short-term solution you can try self-amalgamating tape, it is specifically made to be water-resistant and it forms a good seal. But with a leak like that I'd only recommend it as a stopgap until you can notify the landlord or hire a plumber. A hose like that should not be inside a wall so i'd recommend replacing it with rigid PVC when you can.