Linear Rail Bath
When you buy linear rails you should always wash them in a solvent to remove dried grease or anti-rust compounds that the factory applies.
Using a small bath is an easy, quick and effective way to clean the rails.
Full demo on YouTube...
3D printed bath, the STLs are on Printables at https://www.printables.com/model/252814-linear-rail-bath-clean-your-linear-rails This bath is sized for 150mm MGN7 linear rails but it can be scaled up for larger rails.
Isopropyl alcohol (or other degreaser)
The bath is sized for 150mm MGN7 linear rails, typically fitted to Voron 0.1 3D printers, but it can be scaled up for larger rails. You can scale up the length of the bath in a slicer if you have a longer rail. Or even scale it up in both dimensions for wider rails too.