[dbruce222@gmail.com]

1999 4000 Express here…anyone know what this part is and what’s in it? It’s under the cabin sole, above the aux fuel tank, and plumbed between the master head and y-connection to the vacuum tank. 

Are there duckbills in there or anything I need to clean out occasionally? Gonna replace my duckbills and pump bellow and want to get parts ordered all at once (without unnecessarily taking something disgusting apart!)

There is a duckbill in there. It is only needed if you are using the back head. I have a 2000 and I disconnected my rear head. So I don't bother changing that one when I change my duckbills.
If yo do use your rear head it is a easy change.

 Dave