I've made pouring down on the yeast cake of a prior batch my standard way of making big beers. Now I'm moving into lagers and I want to know if there's any difference. Lagers have a much higher recommended pitching rate, so I'd assume that pouring down is a good idea as long as trub doesn't become an issue.
The pitch rate for lagers is generally twice that of an ale. However, pitching onto a used yeast cake generally results in overpitching by a factor of around 100. Overpitching by this amount is never recommended.
In any case, it does make beer, and works for both ales and lagers with the same effects.
Some people make a 2 gallon batch of lager and ferment it warm, then just pour the beer off the yeast/trub directly down the sink and pitch the "real" lager wort on that cake. I'd say if the original batch was 5 gallons, then split the cake into thirds. Pitch on one and store the other two (after washing) in the fridge for your next lager starter.