In my new home, the bathtub is one of those acrylic insert tub and shower. I noticed that there was dirt/scum on the walls of the shower and tub but didn't know what to use to clean it. I called my mom, since she has a similar tub, and asked her what I should use and she suggested Arm & Hammer Scrub Free.
I needed to pick up a couple prescriptions from Walgreen's so I decided to see if they carried the cleaner and they did. I bought a bottle of the cleaner for $3.99, brought it home and sprayed the walls and tub down. I waited for 3 minutes, the max time according to the bottle instructions, took a damp cloth and wiped the walls down. I was shocked and surprised at how easy the dirt came off the walls.
I did have to use the spray twice since I missed a couple spots when I sprayed the walls the first time and it has a really lemony smell but all and all it works great. You still have to use a disinfectant since this doesn't have any in it but it's worth it if it gets rid of the crud.