Cool!
Now there are three of us that I know of, that have a Sirena. You know, you can just use essential oil in your Sirena. You don't want to use anything that foams. I think Lemon, Orange, Eucalyptus are the best cleanest smelling scents, but you can use others.
T O M -
I don't fill mine past the min line either because that's what the instructions say, but I've wondered what the max line was for (picking up liquid I assume), but if you can pick up water to the max fill line, I would think it's safe to vacuum with the water up to the max line. I don't know.