Whether its the train building, garage or house, eventually the vinyl siding is going to need to be cleaned. Heard this recipe on KMOX Home Improvement Show the other day. Haven’t tried it, but I put it here for future reference. Bob does a great job. 
In a 5 gallon bucket mix-
4 gallons water
3/4 gallons bleach
8 oz. Simple Green
Apply to wet vinyl with brush or by being syphoned through a high pressure spray, but scrub before rinsing. Do small enough area at a time to keep wet until it is rinsed. Protect shrubs and the other stuff she’ll yell at you about.