black tank leak and vent pipes?

[steveirving]

I'm trying to fix a leak which is coming from the metal fitting connected to the bottom of my vintage black tank. The leak seems to be coming from the area with green corrision seem in the pics. After dropping the skin to look in this are I noticed I have two vent pipes coming from the black tank. One extends vertically up from the top and forward end of the black tank out the roof, the other (as seen in the pics) is connected to the dump valve and routes under the subfloor of the trailer under the bathroom sink, and up through the couther top in the batroom.

Is it nessesary to have two vents? Could I just eliminate the rearward one?

Any thoughts on how I should go about fxing the leak (at the green spot) on the black tank?

[dlb435]

Yes, you need both vent pipes. The one for the black water tank you understand.
These trailers were originaly set up to hold only the black water, the grey water was just dumped on the ground or, in some tralers, sent to the black water tank.
If the black water tank is holding only black water it is shut off from the grey water. Thus, the grey water drains need a place to vent or you stink up the trailer.
I have a later model trailer with both grey water and black water tanks. The vents join together and go to a single roof vent.

[Silverflames]

Can't tell from the picture is the tank leaking from the pipes or from the tank itself? I don't like working with the old cast-iron pipes so I would probably change all the cast-iron out to PVC. It will be lighter and easier to work with later down the road. If it's leaking from the tank itself I have used a two part epoxy from automotive store to fix cracks on my old Holding tank. They had a Two part epoxy designed to use on plastics it Looked like a double syringe.