Holding Tank Outside Vent

[CaptDenny]

My 98 Aft Cabin 405 has 2 holding tanks that service our 2 VacuFlush Heads.
I usually have them pumped out at our marina and if I venture miles out into the ocean I can use the OVERBOARD DISCHARGE to empty out. Last time I did this I noticed “poo resido” on the outside of the boat under the vent hole. Never saw this before. Looked at the vent hose from behind my port engine and it looks hard to get at. Or is this an actual problem?
Suggestions please.

[km1125]

Is it possible one or both of the tanks were completely full causing something to splash out the vent while underway? There shouldn't be anything coming out that vent other than smelly air, and using the overboard discharge should have drawn air into that vent. Do you have a carbon filter in your vent line? (that would make it REALLY hard for "poo residue" or anything else to come out the vent)

[CaptDenny]

Thanks KM.
We never let either tank get above half. And looking at the vent pipe from inside the boat I don’t see anything other than the hose going to the vent. Very strange. If I find somebody that is tiny enough to fit back there and cant can’t smell well , they might be hired to check this out.

[g36]

If you already know this I apologize. You are aware that the tankwatch indicators aren't always working properly and may need cleaning.. you mentioned you never go more than 1/2 full how are you telling this? Could you be over filled and the tsnkwatch doesn't show,?. there's no vent filter inline so it will overflow out the vent line. Theres a floor panel just inside the aft cabin at the foot of the bed.. youll see the top of the tank and vent to it. You can remove the line and flush or blow air through it to clear if concerned about build up in it. It's really just a straight shot out the side of the boat.

[km1125]

And if there's no filter in the line then you should be able to put a hose over the vent on the outside of the boat and flush that vent hose all the way back to the tank. Do it when the tank is empty and just do it in short bursts because there is no way for the air to get out of the tank, so pause between bursts to allow the tank to normalize pressure.

[g36]

There is no oem vent filter on a 405. I have added ones to my 405 . Not saying if a previous owner added one but theres not one from carver

[CaptDenny]

Thank You for all your great suggestions. Pulling the vent hose off the tank and blowing into it sounds INTERESTING .
However shooting small bursts of water into the vent from outside ( Or inside) might just help.