The black rubber seal that fits between your dirty water recovery tank tube and the intake to motor. Fits any style SpinsScrub 5 or 6 brush steamvacs. Including new Spin Scrub 50 models FH5900, F5912, F5915 & F5915-930 group. Or the very early models F5800 series like the popular F5855. If your unit has lost a lot of its suction powerthis black rubber boot may be missing. It may have stuck to the dirty water tank once when lifting off to empty and is lost....or, it fell inside the unit some where. Regardless.... when replacing put a drop of contact cement or glue in the area attaching to the motor intake. Just a drop as this needs to be removed to enter the motor area. When sold out the price area will show $00.00 7/27/23 dda