Commonly it's sulphur granules, which come in a tin. They are sold in places that sell gardening products.

But be very careful. I did this several times in my old place, which is where the worst demonic attacks occurred. It was broad daylight in the summer, and I nearly always got attacked quite severely after each fumigation. It did nothing to remove or prevent these entities from coming in. In fact, these attacks got worse after a while, to the point where I was driven out of my house at 3am and then attacked out in the open in the car park.

I even saw the demons with my physical eyes on one occasion. Their aura was so strong that I could literally feel where they were in the room. They basically dwarfed the neg in terms of strength.

I moved shortly after that because the stress of living with these attacks got to me.

Having said that, it doesn't mean that will happen to you. All you can do is give it a go if you choose to, and see what happens.