Poo tank corrosion and sacrificial anodes

[SiFi]

I've two mild steel poo tanks. Is there any virtue in adding sacrificial anodes to the blackwater? If so would it be the usual zinc?

 

I'm minded to add one to each.

[Tony Brooks]

Anecdotally, the contents seem to preserve the submerged parts of the tank, it seems to be the top that rusts through. Unless the top is always wet, I doubt anodes will do much good or be cost-effective. Interested in how you intend to get them onto the inside of the tank.

[David Mack]

When I removed the 30 year old mild steel poo tanks on Belfast the bottom and lower sides were in perfect condition. The top looked OK from the outside, but after the disruption of the removal process shifted much of the rust and paint, what was left was like lace. I assume condensation was the cause, and an anode won't do much about that.

[Machpoint005]

We found exactly this problem in our first boat. 

 

Wonderful stuff, Plastic Pudding. 

 

 

[SiFi]

Thanks everyone, really helpful to hear your comments.  I have access panels in both tanks so I could add the anodes but I do take the point that it is the top that suffers the most corrosion and that anodes would be of little value.

 

I imagine the bottom of the tanks will be pretty anaerobic and won't rust much if at at all. 

[system 4-50]

10 hours ago, Tony Brooks said:

Anecdotally, the contents seem to preserve the submerged parts of the tank, it seems to be the top that rusts through.

OP, read the small print on the tank's warranty: "Invert the tanks every 28 days for maximum tank life".