Whats the best way to clean/wipe/dust the wall behind a toilet tank?

Never occurred to me to do that.

Priti, I use a microfiber duster with a long handle for that. If you want to literally wipe the wall back there, you can use a wet beach towel by sliding it back there from the side of the tank and grab hold of each end and use a windshield wiper motion. That's a bit tricky if you are short as I am (very short) but I go for the duster.....hope this helps...

I bought this set and it's great for getting into those tight places.

https://www.qvc.com/6-Piece-EasyReach-Microfiber-Duster-Set-by-Campanelli.product.V34935.html?upsh=1&sc=V34935-CSWB&TZ=CST

I like to use a fuzzy duster with a handle. But one that is washable is a good idea. There may be some moisture behind the tank caused by the ceramic tank’s sweating, and that makes the dust behind the tank damp, but easy to pick up. Plus, if the duster is something like chamois, you can swab the floor, too, and just wash the duster in the sink. It shakes nearly dry easily, or you can use an old towel to dry it. I hope this gives you an idea for what you can use. ☺️

I put the lid down and sit backwards (so I'm facing the wall). Then I use whatever I need for the job. A duster gets the dry stuff, but if you cut down the handle on a sponge mop, it works great for a more thorough cleaning. The shorter sponge mop is also handy for cleaning the floor behind the toilet.

Use an old scarf...put cleaner on it (Windex is great) drop it down the back of the toilet tank and rub the scarf up and down.

Use a dowel or an old broom stick about 2 inches wider than the toilet. Wet an old hand towel and wrap it around the dowel. Hold the dowel with your hands on the ends and slide it down and up behind the toilet. This allowed you to scrub off the accumulation of dust and dirt. I painted my dowel with high gloss white so I can just wipe it off and keep it under the bathroom cabinet.