450DA head holding tank vacuum vent

[RedRiverRat]

I have been fighting with an occasional bad smell from the head holding tank after flushing. I have determined through trial and error that the smell is venting from what I believe to be the vacuum release valve on the top of the tank. When the tanks are pumped out, this rubber flap allows air to flow into the tank, ensuring the tank does not collapse. This rubber flap should otherwise remain sealed. However, right now when the head is flushed, I can smell immediate purge of fumes from this vent.

So, my question to the group .. has anyone else had this problem? Have you tried cleaning it as a fix? Can it be fixed or is it that the rubber is fatigued and needs to be replaced? If so, how in the heck do you remove it and where can you get a replacement?

Any suggestions / help much appreciated!!

Kevin

 

[Boatingfool]

Have you changed your filter this year?

 

[RedRiverRat]

Yes and no. I removed the filters, checked them and they seemed fine. I blew air through them and it passed without issue. I know the lines to the filters are fine too because I could smell the fumes coming out the ends while the filters were removed.

The smell is coming from the vacuum release vent. Immediately after flushing, the smell purges .. I figure it's while there's positive pressure in the tank.

I haven't checked the lines from the filter to the outside of the boat, I suppose they could be blocked .. but I would think that positive pressure should help seal that vacuum vent, not purge from it.

 

[fwebster]

You don't say what year boat you own. My 450 has completely sealed holding tanks, except for the vent, sender port, waste entrance and waste drains. Where is the part you are describing and a photo would be helpful as well.

 

[Henry Boyd]

I think you might have it backwards. The vacuum vent is there to keep the tank from collapsing when being pumped out. A positive pressure in the tank would actually hold it closed.
What you have described sounds like a dirty charcoal filter. This is a tube, about the size of tube of caulking, with 3/4" plastic hose fittings on each end. One hose runs to the tank, the other end to an above the waterline through hull. Positive pressure from the tank is vented through the hose and filter.

The filter is made of charcoal pellets, once they have become contaminated they stop working. The filter would look like it is ok, but it just won't scrub the stink out.

If you want to DIY, there have been a number of threads posted by folks who have re-charged their existing filters with aquarium charcoal. Otherwise the filter is $ 70- $80.

Henry