I built a cleaner, actually pretty simple. I dont like abrasive material so I use denatured alcohol on a cloth attached to the end of a straight piece of rail.
Power applied to the rail i hold the engine in place while the drive motor spins the wheels on the cloth. Now as not to ruin the wheels im holding I usually disconnect the drive shaft.
I also have used gator clips and held it upside down while applying the cleaner.
One is great for quick cleaning the other required shell opening.
A friend of mine built a cleaner track some years ago after he modeled Conway.
Somehow the locomotive actually went through a little area of what I believe was Simple Green solution about 1/4 inch high then onto a drying section of rail where the engine sat for a day or so. His engines always ran like champs.... I couldnt tell ya how he built it to save my soul.