‘Yeah, well, the more the better,’ said Moody darkly. ‘We're your guard, Potter.’
‘We're just waiting for the signal to tell us it's safe to set off,’ said Lupin, glancing out of the kitchen window. ‘We've got about fifteen minutes.’
‘Very clean, aren't they, these Muggles?’ said the witch called Tonks, who was looking around the kitchen with great interest. ‘My dad's Muggle-born and he's a right old slob. I suppose it varies, just like with wizards?’
‘Er—yeah,’ said Harry. ‘Look'—he turned back to Lupin—'what's going on, I haven't heard anything from anyone, what's Vol—?’
Several of the witches and wizards made odd hissing noises; Dedalus Diggle dropped his hat again, and Moody growled, ‘Shut up!’
Harry Potter and the Order of the Phoenix
"it" in "I suppose it varies" probably refers to "kitchen" in this context. But I don't understand "just like with wizards". Any thoughts?