97 405 Aft Holding Tank Odors/Venting

[Midnightsun]

When you pump out it draws from the bottom of the tank. You need a vent so the tank will not implode from the suction, removing a cap or 2 is only beneficial and cannot interfere in a harmful way. Bottom line is if the vent is plugged then removing the cap makes for a big vent.

[ndunlop33]

Thanks so much for the suggestion, I will check that out when I go down this weekend.

[bud37]

Source of the post Thanks for the replies. I don't know why the pump out guys at my marina think there is only one vent. They did say when they pump it out that they only remove one deck cap at a time because there is only one vent. I don't know if this makes sense to you all ??? There were no inline filters on the boat. I had one installed hoping this would help but it really hasn't stopped the problem. The person I bought the boat from changed all piping to pvc at some point. I have also started using the Noflex Digest so I'm hoping that will help if there is a sludge build up. I will say that when I take the boat over to the pumpout station I don't seem to have a problem emptying the tank. It clears right out. Would this indicate that it's not a vent problem?

I think I know what the pumpout guys were saying now......they were referring to each tank, not both, one deck plate /pumpout fitting and one vent per tank.

There is only a few ways of air to get into a waste tank during a pumpout, because during the pump out the deck fitting has the waste pump out hose attached to it.

One is thru the tank vent , ( consider the pump out hose at 1.5" size and 20" vacuum pulling air thru a 5/8" vent line ??? ), this imo is an issue that has been addressed with the new 1.5" vent lines.

Second can be thru the toilet itself if you have electric macerator.

Now if you have vacu flush there should be a fitting ( vacuum breaker ) on the tank which allows air in to keep the tank from imploding. These fittings are basically some foam and a seal, they can leak and cause a smell to get out of the tank.....you can get replacements from Dometic.

There is no other way unless someone left some fitting loose. Now a significant source of restriction in the vent line can be the vent filter itself if it is not sized properly or it has been installed in the wrong place and the activated carbon has gotten wet, once the carbon is wet it is useless and need to be replaced and the filter installed in a spot where this is highly unlikely.

The digester works well, but the tank still needs proper care and venting. Since you have PVC lines in there ( real good ) , have a look at the filter and that vacuum breaker ( only if you have vacu flush ) I mentioned.

[Midnightsun]

Speaking of Noflex Digester. Here it is impossible to find unless you buy Amazon which sells for $38 + tax. If you have a friend or 2 at your dock that use this, buy a case at following link and split it between you. Much cheaper and you will have a few years supply. Personally I ordered a case for myself and will have a good supply for quite a few years. https://www.jetvac.ca/online-store/Zaal ... p118014859

They also sell it buy the 24/case which is even cheaper but you do need more friends or you must be really full of it

[bud37]

The official name of that vacuum breaker valve is Tank Saver....couldn't remember before......here is a link so you can see what it looks like.


https://www.dometic.com/en-ca/ca/produc ... er-_-25365

[Midnightsun]

Yep, Carver installed one of those on each of my tanks.

[ndunlop33]

Thanks for all the suggestions and the links. I really do appreciate all your help! I will give all these suggestions a try!

[Viper]

Any marina that is a dealer with Western Marine in BC and Transat in Ontario (same company) will have access to Noflex Digester.

[Midnightsun]

Most marinas in my area sell coffee and ice and some even have pop machines.

[tomschauer]

https://www.fisheriessupply.com/zaal-no ... tor-noflex