Removing arm on#88592 to stick thru side of tank

First shut water off at stop than flush all the water out of the tank next take a sponge and get all the water out of tank next unsrew the supply line from the valve under tank than move out of the way next unsrew the nut on the valve of fluidmaster than pull the fluidmaster out of tank stick the new fluidmaster in tighten nut srew the supply line back on turn on stop and let the tank fill up thats it if the fluidmaster dont shut off press the handle let some water out and adjust the fluidmaster screw Tip the water should stop a 1/4 inch below the flush valve tube in center of toilet

Depends on type. Rubber ones usually are suspended from the seat by an arm on either side, you pull it off the arms and replace the same way. Older ones slide down over the overflow tube.

Give it a slight turn to stop it from rubbing on the side

If there is nothing wrong with the fluidmaster, it probably needs to be adjusted, sounds like it is running down thru the overflow tube!

I would put in a FluidMaster system.

http://www.fluidmaster.com/index.asp?bhcp=1

Fluid master comes apart at top.Turn counter clockwise to unsnap .You will see water valve seal. take seal out and clean out any grit. reasemble and should work. hope this helps.

If you are talking about the overflow tube in the tank of a toilet, I would say that it should be cut midway between the top of the tank and the high water mark inside the tank.
The fill valve may even have a mark on the side indicating the high level mark for the backflow preventer.
Gary

Make sure that any valves that you shut to install the fill valve are fully open after the installation.

If that doesn't work, the following is from another fix your stuff site:
Shut off water supply. Lift the rod arm and remove top cap assembly by turning 1/8 turn counterclockwise. Using a straightened coat hanger, carefully clean out the inlet passage of the Valve.

If these don't help, check the model number of your Fluidmaster and include that the next time you write.

This happens over time and also more often if you have hard water. Using cleaner tabs actually make it worse. You need to change it out. Hardware stores carry a direct replacement. I think it was a Fluidmaster 400A model that is identical to yours.

1.The Flapper Valve isn't seating all the way, and allowing water to seep through. (At end of chain)
2.The Fluidmaster water control unit that is connected to the other end of the chain, isn't shutting off when the lever for it, is all the way in the down position.

Test the FluidMaster unit, by lightly applying pressure in a down motion, to that lever.
(Facing the toilet from the front, the FluidMaster water control unit is in the left corner of the tank. {Not trying to insult your intelligence}
The lever I speak of, is the small arm at the top of the FluidMaster. The Flapper Valve chain connects to this lever)

If it shuts off, you may have some fine sand, or other foreign material in the FluidMaster. [Taking one apart, and checking, then reassembling, is No fun!]

If it doesn't shut off when you apply pressure to that lever, you may have a bad diaphragm in the FluidMaster.
Suggest you replace this unit.