Missing something please help

[Strokewitpower]

Not sure but pretty sure there is supposed to be a plug. Bought the truck with a bd trans pan. Got under there to take a look and on the bottom of the bell housing there is a baseball sized hole with threads. I know it should have a plug right? Looks like it's right under the torque converter. Is there any reason this cap would have been left off. I took a pix and will have it up later

[Strokewitpower]

I talked to a friend last night who said that there is a rubber plug that goes there and it wasn't a big deal. I told him I was worried about dirt, dust getting in the transmission he said the torque converter is turing so fast it would blow it out. Someone let me know something please. I am probably still going to get the piece unless there is a reason I don't know of to remove it cause of the larger tranny pan.