Well, what I'd do is mix up a 10% bleach/water mix and pour it in it and slosh it all around top to bottom and sid to side then pour it out and rinse well. Leave the cap off so evaporating "Gases" can be released. I would think once or 2 a mnth would be good, depending on Temps of course and amount of usage. I forgot about the Huskey... that harness looks Good on him too!
As for the water thing, I have seen those and I think they're cool. But it wouldn't work that great for me I don't think. I have a hard enough time walking around here in winter, never mind using a wheelbarrow!
I would definitely go with a garden cart as @CntryBoy777 suggested @NH homesteader. Two BIG wheels on the sides and easy to balance.
For @Alexz7272 I think a nice mushing sled with wheels during non snow season. She has the appropriate "engine" that it is already getting trained to a pulling harness. And boy is he cute!