How can I get rid of dust in the boiler/water tank closet its hard to reach?

Ive been trying to clean the part in my room I looked in as I dont normally go in but it has 2 shelves and the boiler and water tank is inside, my problem is its clogged with over 20 years of thick dust as no one cleaned it before I came and I tried the van but it didnt help that much because the pipes get in the way and I dont want to burst the tank. I attached my bowie knife to an end of a mop stick and scd it out and that working but is they another way? I looked at the floor and they is a possibility of rats breeding inside that room, I always keep it locked and nothing inside however but they seem to be biting the floor on the wood. Help please