[wingnut60]

I believe it is a common size--somewhere else here or on the SOITC site there is a discussion of the extension tool supplied with some of the newer units. Should be a covering on the pump that is removable--take it off and try some bits to get the size.
If you can't figure it out, I'll be back home Friday and let you know.
If you happen to have the gen prep package, there is a removable panel just opposite the pump end on the gen wall that is used to access the pump.
Joe