little rubber cup came out of fuel tank

[Sam I Am]

I have been having fuel delivery issues.
Today I took out the in-cab (only) tank in my "71, dumped the gas, did the swish and spit twice, then took it down to the car wash and douched it out with the pressure wash.
As it was draining at the car wash, I found a little rubber cup that was blocking the fuel sender hole. I don't have a camera or I would show a picture of it. It is about an inch and a half around with about a quarter inch lip and about an inch and an eighth deep. And it was inside my gas tank!
I'm not sure if this might have been blocking the fuel pick-up tube when the tank got low. Something was, because I wasn't getting fuel and both filters were clean.
I just now got the tank in and put gas in the truck. It is outside idling now, so hopefully I got out the worst of the sediment or other blockage.

Any ideas about that cup?

[DuckRyder]

It sounds like the cover for the sending unit float.

I have no idea why they put them in there.

[mrtleavitt]

Ya that's what it sounds like. You'll be fine w/o it in there, most of them deteriorate (?) and come apart. Could have been you problem.