[MC1600]

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!)

[ReelMagic]

It looks like a Domenica Standard 1.5" Inline Check Valve. (Back-flow Prevention) which uses 1.5" Duck Bills

[MC1600]

So the only attention it needs is getting it out of there and replacing the duckbills?

[ReelMagic]

believe that is correct

[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

[MC1600]

Thanks Dave. While I have you…there also appears to be a duckbill holder on the underside of my vacuum tank, is that the case? So by my count, the whole system needs 6 (4 at the pump, 1 at the check valve, and 1 under the vacuum tank)?

[MC1600]

Just to close the loop on this, there are six 1.5" duckbills in the 4000E with the aft head; 2 on each side of the pump, one in the check valve mentioned above, and one more at another check valve under the vacuum tank (the latter of which is a %$*&^ to get to!