My hotel is near Vallinn Valikko and the journey planner recommended catching tram 6T from the Ferry terminal...nice to know it's near a depot.
Are the day tickets valid till end of service or 24 hours from validation?
Trams only go to the depot when they need to go there and not as part of the normal day's routing. There is no tram stop there anyway and 6T isn't a normal working so I'm not sure why you've been told to use that. Tram 9 actually leaves outside the ferry terminal...getting to the 6's stop is quite a walk even if you know where you're going - that area of Helsinki is in the process of being converted from a harbour to a residential area so there's a lot of building and road works. Use the links to the HKL route planner from earlier.
Tickets are valid 24 hours from first usage. Make sure that you "check-in" when you get on the tram otherwise the ticket isn't valid and Helsinki's ticket inspectors can be merciless. IIRC, you get an electronic ticket which is shown to the reader just inside the doors of the tram - it has a small display, lights and four buttons. For a time based ticket you don't need to press anything and you should get a green light after holding it against the reader for a second. Any problems speak to the driver - who all invariably speak English.
If you're looking for tram action forget the depots - nothing to really see there, but just go to the city centre where all the lines more or less meet. If you want trains then there's a nice walk from the central railway station through the parks next to the line and be amazed at what broad gauge and a huge loading gauge will get you...
t
Ian