Since the original thread on holding tanks has gone off on wild personal issues, I thought I would add some information.
Just for a bit of background, I earn my living from process equipment for sludge handling.
The first rule in large-scale sludge handling is "never hold sludges". Clearly where we have a holding tank, we are breaking that rule.
The next rule is that if you want to minimise odours, you need to keep the sludge aerobic, meaning keeping some oxygen available for the bugs (microscopic creatures), that will be in the seawater and sludge, and dining on your sewage. If you're sailing, the constant motion of the boat will stir up the surface of the tank, and provide some aeration. Unfortunately, this won't happen if you are tied up to a marina or a calm mooring. Composting toilets have a mixing handle to provide some aeration. Not really practical in a holding tank.
The last important rule is, if there is no stirring of the tank, sludge will settle in the bottom. In large-scale plants, we have scrapers to move the sludge towards the outlet. The sludge settling is what I believe is the problem in SouthAce's original post.
So what to do? The best practical solution appears to be to arrange the inlet piping such that the incoming waste stirs up the bottom of the tank. The incoming waste will contain some oxygen as well. When discharging at sea, you could continuously flush the toilet to assist in the discharge.
A more complicated solution would be blowing air into the bottom of the tank, or miniature aerator mixers, but that would only be for retired municipal engineers with nothing else to do. Another practical, but complicated, solution would be a recirculating pump, dropping some of the feed back into the tank at a high level in order to get some aeration and mixing.
My conclusion-get a composting toilet.
Well I finally got my holding tank installation finished today. All seemed good with a gravity dump if environmentally/ legally possible and easy access to the pump out outlet and a huge 38mm vent hose.
As I said, all seemed good, until I filled it with 30 odd litres of sea water and discovered one of the hose fittings has a one drip every 30 - 45 seconds leak.
Arrr!
Select to expand quoteJethrow said..
Well I finally got my holding tank installation finished today. All seemed good with a gravity dump if environmentally/ legally possible and easy access to the pump out outlet and a huge 38mm vent hose.
As I said, all seemed good, until I filled it with 30 odd litres of sea water and discovered one of the hose fittings has a one drip every 30 - 45 seconds leak.
Arrr!
Be happy-its only water!
Select to expand quoteJethrow said..
......... one of the hose fittings has a one drip every 30 - 45 seconds leak.
Arrr!
Can you pour hot water over it (or use a heat gun) to soften the hose & then tighten it up a bit more??
Select to expand quoteYara said..
Since the original thread on holding tanks has gone off on wild personal issues, I thought I would add some information.
Just for a bit of background, I earn my living from process equipment for sludge handling.
The first rule in large-scale sludge handling is "never hold sludges". Clearly where we have a holding tank, we are breaking that rule.
The next rule is that if you want to minimise odours, you need to keep the sludge aerobic, meaning keeping some oxygen available for the bugs (microscopic creatures), that will be in the seawater and sludge, and dining on your sewage. If you're sailing, the constant motion of the boat will stir up the surface of the tank, and provide some aeration. Unfortunately, this won't happen if you are tied up to a marina or a calm mooring. Composting toilets have a mixing handle to provide some aeration. Not really practical in a holding tank.
The last important rule is, if there is no stirring of the tank, sludge will settle in the bottom. In large-scale plants, we have scrapers to move the sludge towards the outlet. The sludge settling is what I believe is the problem in SouthAce's original post.
So what to do? The best practical solution appears to be to arrange the inlet piping such that the incoming waste stirs up the bottom of the tank. The incoming waste will contain some oxygen as well. When discharging at sea, you could continuously flush the toilet to assist in the discharge.
A more complicated solution would be blowing air into the bottom of the tank, or miniature aerator mixers, but that would only be for retired municipal engineers with nothing else to do. Another practical, but complicated, solution would be a recirculating pump, dropping some of the feed back into the tank at a high level in order to get some aeration and mixing.
My conclusion-get a composting toilet.
Many thanks Yarra for starting afresh ( maybe not the best discription ) it is going to be an on going topic as marine pollution becomes more in focus.
I read a post of Peggy Halls suggesting that adding nitrate to the holding tank has an oxygenating effect, some chemical reaction that your probley more aware of than I.
My issue was with the commercially avalable activated carbon filter. ( had no idea how much s**t would hit the fan ) Should get the chance this weekend to put a diy filter together.
P.S. Composted would be the way to go especially if you have the same system at home
Select to expand quoteLazzz said..Jethrow said..
......... one of the hose fittings has a one drip every 30 - 45 seconds leak.
Arrr!
Can you pour hot water over it (or use a heat gun) to soften the hose & then tighten it up a bit more??
Yeah Lazza, that was my plan. The thing that really @#$%s me is that the leaking hose is the only one I didn't replace! 
Interesting that a pure technical thread does not get much interest, but throw in clashing personalities and a thread fires up. Bit like reality TV.
However, this is a very serious topic. It can kill: www.abc.net.au/news/2019-02-04/sydney-party-boat-had-unsafe-gas-levels-before-death/10776366
To keep those gases down you need either toxic chemicals which are a problem themselves, or aeration. As I have noted above, organising aeration on a relatively small boat has lots of complications. Blowers are noisy and need power.
We need a heap more pump-out stations.
I heard they had plumbed the pump out into a exuast outlet from a main engine a few weeks before this incident?
Select to expand quotesouthace said..
I heard they had plumbed the pump out into a exuast outlet from a main engine a few weeks before this incident?
They are talking about Hydrogen sulphide.
www.news.com.au/travel/travel-updates/incidents/police-and-maritime-officers-raid-cruise-boats-following-death-of-woman-in-toilet-cubicle/news-story/bdba6da026f641633d17055633100370
Well I'm happy to report the new holding tank survived the Easter long weekend with flying colours. Nothing had to be sealed in buckets so the wife is happy and keen to do it again, so I'd say that's a win all round!
