Black tank odor - switch to macerating toilet?

belfert · October 16, 2019, 01:40:07 PM

Quote from: buswarrior on October 16, 2019, 08:32:39 AM
Multiple little things adding up?

The drop from the toilet shouldn't be the highest opening in the tank, the vents should be. How far do each protrude into the tank top?

I have a 100+ gallon rectangular waste tank made of stainless steel. Both the vent connection and the toilet connection are simply female fittings welded to the top side of the tank so they are both at the same level. I suppose I might be able to have a pipe or tube welded in so the toilet waste drops further in. The issue there would be if the tank ever filled up close to that pipe/tube I would have a mess. I would end up with nasty stuff all over the outside of that pipe/tube.

chessie4905 · October 16, 2019, 03:10:45 PM

I'm missing something. It should only go into the tank about 4 inches. Be a good gauge when it is getting full. No need to weld a sleeve. How about thinwall pvc of the size to slip inside the welded sleeve? You could glue it into place. Maybe Gorilla glue or Shoe Goo. Many fuel tank filler necks are designed that way.

belfert · October 16, 2019, 04:19:08 PM

Quote from: chessie4905 on October 16, 2019, 03:10:45 PM
I'm missing something. It should only go into the tank about 4 inches. Be a good gauge when it is getting full. No need to weld a sleeve. How about thinwall pvc of the size to slip inside the welded sleeve? You could glue it into place. Maybe Gorilla glue or Shoe Goo. Many fuel tank filler necks are designed that way.

See the attached photo. The connection at the tank is threaded. The right side connection eventually goes to the vent. I have a smaller connection on the top of the tank on the far side of the tank that was/is intended to be the vent, but it is plugged right now.

I did lots of research before doing my plumbing and never heard of placing the toilet pipe down into the tank until today. I would have designed the tank differently if I knew that back then. I might be able to get a pipe 4" into the tank, but I'll lose close to 25% of tank capacity.

chessie4905 · October 16, 2019, 04:36:00 PM

You won't lose any capacity. Level will still rise in extension as before without. The liquid will still seek level. Just like in a gas tank.

chessie4905 · October 16, 2019, 05:00:49 PM

That's the good thing about usuing pvc. You can pry it out if it doesn't work for you. Start with a 2 1\2" stub first.

Geoff · October 16, 2019, 05:04:39 PM

Quote from: belfert on October 16, 2019, 04:19:08 PM
See the attached photo. The connection at the tank is threaded. The right side connection eventually goes to the vent. I have a smaller connection on the top of the tank on the far side of the tank that was/is intended to be the vent, but it is plugged right now.

I did lots of research before doing my plumbing and never heard of placing the toilet pipe down into the tank until today. I would have designed the tank differently if I knew that back then. I might be able to get a pipe 4" into the tank, but I'll lose close to 25% of tank capacity.

Hum, my black tank vent is just like yours, only it attaches to the grey tank vent at the same level using a tee. So this way if the black tank over flows, it goes into the grey tank. I have never over flowed the grey tank.

Scott & Heather · October 16, 2019, 07:30:58 PM

This thread is cracking me up. I especially liked the idea of lighting an open flame at the top of the vent Hahahah. Chessie...

You just can't eliminate the smell when flushing while underway. But I can tell you that the toilet in my master half bath doesn't stink nearly as bad when we flush as the toilet in the guest bathroom. That one has a straight drop whereas my master bath toilet actually has a three foot horizontal run before dropping in the tank. That actually makes a difference believe it or not

dtcerrato · October 16, 2019, 07:46:06 PM

Hey Scott forgive me for saying this but that's like saying your $#!% don't stink! Lol

DoubleEagle · October 16, 2019, 08:05:42 PM

In New York State, back in the 1970's, at least, the plumbing code for residences required a fresh air inlet (four inch pipe if the drain was 4") to be located near the point where the drain pipe exited the foundation. This enabled a flow of air through the drain pipe and up the vent stack. This principle might work in our buses as well with an inlet vent just above the tank on the side of the bus, and then a vent stack up through the roof. A booster fan should help the process, but might not be necessary.

The rationale for having the RV style toilets right over the tank is probably because of the small amount of water used, and the chances of deposits building up in horizontal pipes. In house plumbing, the slope of the pipe is one-eighth inch per foot, because a steeper slope allows the water to run off more quickly, leaving the solids behind. In our situation, with less than level conditions often, finding the correct slope is more difficult. Maybe a home style low water toilet right over the tank with large air intake pipes, and vent pipes, is the best solution. We need someone to test this and report back!

Jim Blackwood · October 16, 2019, 08:27:55 PM

You know what is amazing to me? City sewers are. Now you would expect them to stink like your holding tank, right? And to be fair they ain't no flowerbeds. But they don't stink anywhere near as bad as you would expect. Certainly tolerable for anybody to put up with for an extended period if they must. By no means pleasant mind you, but nowhere even remotely close to what blows out of the RV toilet. Also what runs through 'em is a surprise. You never see any brown trout or other lumpiness washing by, it's all dingy water and some grease build-up in places, along with a fair bit of gravel, maybe some rag, and the occasional ring. What the heck is up with that? Apparently everything liquefies by the time it gets to the curb. How's that for a surprise?

By comparison a RV blackwater tank is a seriously nasty, nasty place.And there's got to be a reason for that. Apparently it's totally a matter of letting the air get to it, well that and letting the gas get away I suppose. But the good news is that if they can do it we can do it. It's just a matter of figuring out how.

Jim

Jcparmley · October 16, 2019, 08:33:45 PM

I'm planning on using a flushmate pressure assist toilet that flushes 1.0 gallon per flush. It will be installed directly above the black tank. It has a sealed tank so no problem with water sloshing in the tank and it should do a good job keeping out odors due to some water in the bowl. I hope this is a good plan.

Quote from: Scott & Heather on October 15, 2019, 11:31:08 PM
Don,

1.28 gallons per flush...we have four people living in our bus. That's four flushes first thing in the morning, and several sets of those throughout the day. If each of us only flushed three times a day (and I'm telling you, we flush more than that) the 100 gallon tank would only last around 6 days. That's not enough for us when we are traveling heavily or boondocking in a parking lot. And in real life practice the tank only lasted about 4 days. Just not enough. And chessie, there ain't no house toilet that flushes only a quart or two. 1.28 gal is The minimum. Rv toilets actually do flush only a quart per flush. Literally 1/5th what a house toilet flushes.

Toolman · October 17, 2019, 01:48:25 AM

The answer is very simple

, I pump a small amount of compressed air from the bus into my tanks while driving
I also vent my tanks ( 40mm ) back to a venturi in the engine air intake, before the air cleaner.
I also have a small fish tank air pump that I can use if stopped for some time. the air is pumped in the bottom of the tanks and bubbles up through the contents = no smell

richard5933 · October 17, 2019, 03:26:27 AM

Quote from: Toolman on October 17, 2019, 01:48:25 AM
The answer is very simple , I pump a small amount of compressed air from the bus into my tanks while driving
I also vent my tanks ( 40mm ) back to a venturi in the engine air intake, before the air cleaner.
I also have a small fish tank air pump that I can use if stopped for some time. the air is pumped in the bottom of the tanks and bubbles up through the contents = no smell

Interesting what you say here, especially considering what chessie4905 posted in another thread about the OEM air cleaner on the Buffalo buses. Apparently there is a 2" tube running from the holding tank venting system to the air cleaner. Whenever the engine runs, it is sucking from the holding tank's vent and pulling the odor into the engine.

Maybe that's the answer to keeping the black tank from releasing odor when flushed while underway. Route a piece of tubing from the vent to the engine air cleaner. I know, our tanks are much further from the engine the the factory bathrooms, but something along those lines obviously would work or the factory wouldn't have wasted money doing it.

chessie4905 · October 17, 2019, 04:33:27 AM

If you have all that odor when you flush, then your vent is too small.
Of course city sewer don't smell as bad. The water compliment of the sewage is far higher, and includes grey water.

Jim Blackwood · October 17, 2019, 07:22:57 AM

Quote from: Toolman on October 17, 2019, 01:48:25 AM
The answer is very simple , I pump a small amount of compressed air from the bus into my tanks while driving
I also vent my tanks ( 40mm ) back to a venturi in the engine air intake, before the air cleaner.
I also have a small fish tank air pump that I can use if stopped for some time. the air is pumped in the bottom of the tanks and bubbles up through the contents = no smell

Some real good ideas right there. I like the fish tank pump idea, never thought of that one. Running the vent to the air cleaner is good too, sorta like propane injection!

The compressed air leak is a no cost option too, do you run that into your bubbler for the fish tank pump?

Even with all that I also think it would benefit from a second vent, maybe to the roof with some active means of creating airflow just to scavenge the tank.

Good point about the extra water in the city sewer. Maybe that's a vote for combined tanks, or at least extra water when flushing.

Jim