How evil are flexible bladders really?

[Doug Snell]

I have a flexible bladder on my boat now which is emitting a very foul aura, but I'm assume the crust buildup around the bladder inlet fitting (a possible freeze/thaw victim from this past winter) is the cause of the odor.My question is if a flexible bladder has an inlet and outlet fitting (1-1/2" each) and a 5/8" vent line fitting, and I still depriving the contents of the air it needs for the arobic bacteria to do their thing? Is it a matter of not suppying air to the interior, or do you need the dead volume above the contents that a hard tank provides so nicely?Doug Snell

 

[Peggie Hall/HeadMistress]

Bladders not a good choice...

As you're seeing, they're highly prone to leaking around fittings and because they're designed to "hug" the contents, preventing foul odor out the vent is all but impossible (the air space above the the contets is necessary). It's also almost impossible to secure a bladder so that it doesn't move at all...and even the slightest movement chafes it. Life expectancy of bladders isn't much better than that of a metal holding tank...about 10 years for metal, only about 15 for a bladder...compared to several decades for a good quality thick-walled plastic tank--which usually costs less than metal or a bladder.