he has been tested for worms, and had his scent glands cleaned already.

He does it to dry it after he pees or to scratch it.

MAybe after he goes to the bathroom it sticks to him so he wipes it off on the carpet. Thats what my puppy did! :

I would say that his butt itches. Sometimes mine do that when they have some poop left on their butt or when their butt glands need to be expressed. Many dogs express their glands on their own by dragging their butts.

He may have a rash, infection, etc. My cat did this, and it was an infection, so the vet prescribed medicine for it, and it stopped.

he might just do it for fun. because my dog has been tested and she still does it. She only does it when shes bored so that's what i think

my dog does that aswell her glands are ok and she is upto date with worming. i think she just does it to clean her bottom or maybe she sometimes has an itch.
its not very funny when she comes in and has a bit off mess on her bottom and decides to clean it on my carpet, although she thinks it is.
i think some dogs just like to make sure they are clean.
my male dog had an infection of the anal glands and never scooted his bottom on the floor.

He's leaving skid marks on your floor.

He might be allergic to something, I suggest you take him to the vet so they can give him something to stop it.

There is some build up that is anooying him. To make him stop place him in your bathtub. Look at his butthole and sqeeze the sides of the butthole. Some liquid shud shoot out. If it does then he will stop. hope this helps

they have glands in their butts and they need them cleaned. my dog does the same thing. it itches them before and after they get cleaned. take it to the vet or the groomer and they will take care of it.

maybe his butt itches, i am not being sarcastic, no joke

It could be that its something he is taking or being washed with. I would get some non perfumed wash and scrub him really good. My dog does this somtimes but its just my sign that she needs a bath.Also if he just got some shots he could be alergic to them so just in case i'd ask the vet. Hope this helps!

He has an itch on his butt or maybe he needs to use the restroom?

It may be that he is cleaning himself after peeing or pooing, maybe a little rash, chk for redness,or it does sound like anal glands are full, these are scent glands inside the anus, they fill with fluid every few months, most dogs get this prob from time to time, the vet or groomer will evacuate the for your dog....rubber glove job :-)Or you can get a piece of tissue and get somebody to hold him, lift his tail high, and squeeze his area together GENTLY.if a liquid comes out quite easily...bingo....its the glands that are full.....be prepared for a very stinky smell. Im a vet nurse and groomer, done it hundreds of times....if in doubt, go to vet, only takes 5 mins to sort it.

i heard something before about this that when dogs do this they are either rubbing their scent or either it itches him hope this helps

Maybe it feels good, lol! :-D

He might have worms, dogs rub there butts when they have worms.Next time he goes to the bathroom look at his stool and see if there are any worms in it.He probably just need deworming.

Your dog is scooting possibly because his anal glands are full and need to be expressed. Please ask your vet to do it if you've never done it before. If his diet is regular with dry kibble food, it should make expressing his glands on his own from the thickness and bulk of his stool. If you're feeding your dog canned food, it doesn't offer the bulk/fiber he needs to have a firm stool.

Here's a link about 'anal glands': Anal Glands - structure, impact and expression