Technical Gas tank question

I removed the gas tank from my 37 Caddy today as it has been sitting for a long time. The tank is not stock ,,appears to be a cutlass/skylark type tank that would have had the filler behind the tag. Anyway, there is a clunking noise in the tank, I took out the sending unit to look in and there is what looks like one of my dogs bowls, a round metal bowl looks about 6" diam. and a couple of inches deep in there. Tank is surprisingly clean from what I can see inside, but can you tell me what the big dish is. It sure didn't get in there through the sender or fill hole! Thanks , D.

 

Anti slosh shield....or you dog lost a bowl.....

 

^^^ They are attached by various means to the tank base around the pick up to maintain a reservoir of fuel during braking, cornering, acceleration.

 

Tanks for reply, I'll have to talk to a shop about how to attach it .

 

Apparently the thing to do is drill a hole through the "dish" and tank and put in a sheet metal screw, then solder it - so it won't leak.
Any other ideas or? Thanks, d