The BACKWASH PLUG should have a small number on it. The number matches the diameter ( in inches ) of your resin tank. The most common is 9 ( for 9" x 48" tanks ). Thus the part number would be 25F-9.
Injector Caps may have a letter "A", "B", or "C" on them ( older versions ), or none ( newer Versions ). They used to be Black in color, and newer versions are Gray in color.
Large Injector Cap for Autotrol Models 255, and 268..
Older injector caps ( 8F-BB ) and screen caps ( 7F ) can be remove with a standard flat head screw driver.


How do I remove the Backwash Plug or the new Larger Injector and Injector Screen Caps ( used on Autotrol 255 and 268 )?

A large ( 1/2" ) flat head screw driver or a # T50 "Star" torque wrench will make the job of removing the Cap / Plug easy.
* ( We do not sell the T50, but every hardware store should have available, if you need / want one ).
And you would want to have the Water OFF before attempting to remove any plugs or caps on your valve body.
You can put valve into "Backwash",
or simply push one of the back Valve Discs open with screw driver for 5 seconds ( after turning water off )
to relieve any pressure in the valve.

See the Star Wrench Tool below,
Star WrenchT50 Wrench