Replace Vetus black water tank fitting

[Star stream]

Hi,
Any advice gratefully received on this one.
I have a black water holding tank with a broken vent hose connector so need to replace the Vetus tank fitting.
I have no access hatch and the existing fitting looks like it is installed with access from the inside. How do I replace this fitting or do I block it off and install a separate vent?
Thoughts please?
Kind regards

 

[PCUK]

It looks as if the centre could unscrew? Or is the whole fitting just screwed in from the outside. Have you tried unscrewing the screws?

 

[Star stream]

Hi pcuk
Thx for viewing the post. The main body of the fitting has an internal flange and is inserted from the inside (presumably during construction) and the outer ring you see in the photo screws onto the main body by hand from the outside to hold all in place. I could unscrew the outer ring and push the fitting into the tank and leave it there but not sure what to replace it with. Also thought about cutting the flange flush and trying to glue a spigot in its place or blanking the whole lot off and inserting a vent elsewhere.
Any suggestions gratefully appreciated. Kr

 

[Boater Sam]

A Brass Essex fitting can be installed from the outside with no internal access. Available in many sizes, you could fit one in the remains of the original fitting.

 

[PCUK]

Sometimes these inner flanges have a slot cut into one side to allow it to be fitted from the outside. Worth having a look. I personally doubt that the fitting would be inserted during construction.