They like to burrow - so if he hasn’t returned from whence he came, he may have found something nice in which to hide. Like a pile of clothes. Or under a bean bag*. Or his new abode is in that giant mound of soil you put in the back room and forgot about.
Blue tongues are territorial. So he’ll want to be getting back home. Maybe after a beer.
*That would be terrifying. Seeing a bean bag I mean; not the finding of a lizard under it.
Treat it the same way you treat in-laws.
Give it 3 days to leave on its own, after that kick its ass out to the curb.
Well, that’s pretty neat… yeah it’s fuckin’ nifty.
That’s what you get for heading back to Australia, but at least you found the least deadly life form there. Stay away from its mouth if you do grab it (and it looks like a long neck, which means it could reach far around), and don’t grab it by the tail.
I thought you grew up in Australia. Haven’t you ever seen a blue-tongue before? We used to catch them all the time when i was a kid, along with bearded dragons.
If you want to move it outside, you should be able to grab it just about at the forelegs with one hand, and further down the body with your other hand so you don’t injure it. Don’t crush the legs; give them a place to protrude between your fingers. As long as your top hand is just behind the neck, it shouldn’t be able to turn and bite you.
They are completely harmless, and can’t injure you in any significant way, but a bite on the finger can be a little bit painful as their jaws are pretty strong.
In case you didn’t recognize them, they’re the lyrics to a Dead Milkmen song, Big Lizard in my Backyard.
I just came in to post this. 
I’m not all horny for reptiles, but they don’t bother me, in general. I’d let it find its way out by itself.
Joe
I’d like to say keep it- but it’s actually illegal to keep wild caught ones, and you even need a license to buy one cite
Try and trap it, and release it somewhere a little way away; they generally like hot spots, especially in the morning. I’ve worked with them in a zoo in the UK. Alternatively, that site also has a list of people licensed to catch and release reptiles- here (PDF warning).
Oh, and if you kill it- yourself, or get a neighbour’s pet to do it, I will personally fly over and slap you silly with a wet haddock. They’re lovely little lizards.
I’d probably wait till he goes outside then shut the door on him.
It won’t have anything to eat in the house so it will (at the very least) need to go outside to hunt. If it has found a nice spot in the house it will want to stay there and just commute in and out every day, but that may not be practical ie if you close all doors and go away for a while what’s he going to do? They are quite persistent commuters. We had one about 50% bigger than yours at our previous house who would make a regular daily trip from almost one end of our block to the other, presumably to go from its favoured sleeping spot to its favoured eating or sunning spot.
And as someone said above, they are territorial and they really, really don’t like being uprooted once they have chosen a spot. I had a pile of wood and junk and dirt in our yard from when I renovated a shed. A few months after the renovation I found the time to clean up the pile. There was a large bluetongue in residence. He really didn’t want to go. Long after my removal of 90% of the junk should have made it clear to him that, sadly, his home was gone he just stayed in the spot hissing at me and glaring at me and showing me his tongue and chomping on my boots while I removed the final 10%. Poor fella. Anyway, plenty of other spots in the garden for him to go to.
They luuurve snails. Put one in front of him and watch it vanish. I used to feed them to a monster blue tongue that lived under a retaining wall when I was a kid. I’d put one down a foot or so outside the crack in which he lived and a few seconds later (presumably by smell) he’d know to come out and grab it.
So you all say they are harmless but they can bite you and cause pain? That to me isn’t harmless. It’s like saying, let the bed bugs stay because they don’t spread disease, they just make you itch. Ewww to bed bugs and ewww to lizards. Unless the lizard is eating the bed bugs 
Wikipedia redirects blue tongued lizard to blue tongued skink
hey are relatively large lizards (up to 45 cm total length), light-bodied, short-limbed, broad
(45cm = 17.72 inches)
Well, cats can bite you and cause pain, but I still regard them as harmless to human beings. (But not to small rodents and birds.)
Where is the option to scream and run?
Analogy fail.
And i meant harmless in the bigger picture sense. Yes, if they get your finger in their mouth it stings a bit, but the worst case scenario is one where you pull your hand back quickly and shake it for a couple of seconds, then forget about it. There is no venom, and (at least in my experience) they don’t even break the skin, so there’s almost no chance of infection; it’s basically like a sharp pinch.
In the world of Australian wildlife, that’s damn near friendly.
Dammit y’all, I thought I was going to saunter in and be original.
As for lizard poop - I think it’s safe to say that, since you are in NSW, it probably contains the shoes of toddlers and remains of infant jewelry.
I’m just going to say to those who find random lizards in their houses:
You are so f-ing lucky.
This winterized Canadian would think it’s the coolest thing in the world. Hell, I get all excited about seeing green anoles when I visit Florida.
I’m going to agree with the other posters who say just leave him alone until he leaves on his own accord. But first take pics. “When come back, bring pics.”
A couple of years ago, a friend of mine called me over to get one out of her house. They aren’t poisonous, but I thought a bite would require me to get a tetanus booster or might lead to an infection. I threw an old towel over the lizard as a precaution, then picked up the lizard and put it in a box. I took the box outside, put it on its side and let the lizard walk away at its own leisure.
More recently, my dogs killed one in the backyard. I wouldn’t recommend getting a neighbour’s cat or dog – they would probably do the same. Not only would a harmless and beneficial animal die, you would have to clean up the mess.