Hi- just got this unit BUT was never installed, so "like new". Problem is a missing a part (see photo) The "piece" is round with a slot on the bottom and a screw to secure it on top- connects to the drain. Can’t find a diagram showing the parts for this unit. I took it to a plumbing supply store today and showed them the disposal, they said the part should be the same as on other models that are close to the 175.60505. Any suggestions where I can locate this part...or at least the part number? Thanks!