Why is my toilet bubbling?

[HeadMistress]

Dear Peggy (or others),


But, two out of three heads (Dometic 8700 Masterflushes) started bubbling a lot a few seconds after flush, soon after the hoses were replaced. I'm aware that he changed anything related to vents. The timing could be coincidence. And we don't use a tank. It all gets pumped straight through the seacocks (one for each toilet). One of the bubbling toilets is above sea water, the other is below.

Any idea what the problem is? The hoses are new, as mentioned, but the blackwater also passes through some old PVC pipes in some places. So it's possible the PVC or toilet parts are dirty. Could that cause bubbles? My plumber thought it might be the parts of the toilet are dirty and said we could open it up to check. I can do that but wanted to see if that sounds like an accurate diagnosis or not first.Thanks in advance
Will

Since the hoses are new I think we can rule out sea water mineral buildup in them. A blocked or partially blocked holding tank vent is the most likely culprit. That would pressurize the tank enough to create enough back pressure to cause the toilet to bubble and "burp" when flushed.

There could be some mineral buildup in the toilet plumbing, but it's definitely NOT necessary to take the toilet apart to clean it. Muriatic acid--available from any hardware store--will dissolve mineral buildup (read and FOLLOW all directions for safe handling!!!)...a weekly cup of distilled white vinegar (available from supermarkets) will prevent it. Cut off the flushwater intake to add it. Follow with clean FRESH water after 45-60 minutes. Even though the muriatic acid isn't needed in new hoses, it won't hurt them to run it through them 'cuz that will send it through the hard PVC pipe where it may BE needed.


I also recommend that you flush a quart of clean FRESH water daily to clean out the toilet and piping behind flushes.



--Peggie

 

[Sea Q]

I have 2 of the same units (great units) and never had that problem. Your best to check with the manufacturer . Just a wild guess (since you go direct overboard) is there a loop in the discharge hose to make a liquid trap to stop any air pumped down the fitting from coming back after the pump stops .

https://www.dometic.com/externalassets/dometic-masterflush-8743-macerator-toilet_62762.pdf

 

[willd]

Greetings,
I'm surprised no one has mentioned this yet...

The only place you can still get gas for less than $2....

 

[willd]

Since the hoses are new I think we can rule out sea water mineral buildup in them. A blocked or partially blocked holding tank vent is the most likely culprit. That would pressurize the tank enough to create enough back pressure to cause the toilet to bubble and "burp" when flushed.

There could be some mineral buildup in the toilet plumbing, but it's definitely NOT necessary to take the toilet apart to clean it. Muriatic acid--available from any hardware store--will dissolve mineral buildup (read and FOLLOW all directions for safe handling!!!)...a weekly cup of distilled white vinegar (available from supermarkets) will prevent it. Cut off the flushwater intake to add it. Follow with clean FRESH water after 45-60 minutes. Even though the muriatic acid isn't needed in new hoses, it won't hurt them to run it through them 'cuz that will send it through the hard PVC pipe where it may BE needed.


I also recommend that you flush a quart of clean FRESH water daily to clean out the toilet and piping behind flushes.



--Peggie

Thanks Peggie,

I flush with fresh water. The holding tank is bypassed, so it all goes straight out the seacocks.

Perhaps that is why we get bubbling: Without a holding tank involved, there is no vent involved, so the only place to air to enter the hose is from the toilet bowl? If this makes the most sense, is there anythign that can be done about it? Can/should I introduce a vent somehwhere in the system? Or a loop/rise? (One toilet is above the water line and has a hose/pipe system that falls constantly toward the seacock; one toilet is below the water line and has a rise in the hose to take it breifly above the water line; both toilets bubble).

It is just odd that we got signficantly worse bubbling after the hoses were replaced (there was a little bubbling before, but it could be avoided by prefilling the bowl with more water; no longer, no amount of water in the bowl stops the bubbles). Also odd is that one of our three toilets (which also goes direct out a seacock) doesn't bubble hardly at all. Perhaps the plumbing valves and connections are just not quite as tight for that toilet and so air is seeping in from elsewhere? It also has a shorter throw to the seacock, and it's been used the least over the years (especially before we bought it).


Will

 

[willd]

I have 2 of the same units (great units) and never had that problem. Your best to check with the manufacturer . Just a wild guess (since you go direct overboard) is there a loop in the discharge hose to make a liquid trap to stop any air pumped down the fitting from coming back after the pump stops .

https://www.dometic.com/externalassets/dometic-masterflush-8743-macerator-toilet_62762.pdf

One toilet (which is below the water line) has a rise in its hose briefly above the water line. One toilet (which is above the water line) does not have a rise.

Are you suggesting a loop (or what I'm calling a rise--same thing right?) might help or might be the source of the problem?

Will

PS - as you've got the same system, have you by chance come across a way to get them to automatically pre-fill with more water?

 

[twistedtree]

One toilet (which is below the water line) has a rise in its hose briefly above the water line. One toilet (which is above the water line) does not have a rise.

Are you suggesting a loop (or what I'm calling a rise--same thing right?) might help or might be the source of the problem?

Will






PS - as you've got the same system, have you by chance come across a way to get them to automatically pre-fill with more water?

For your below water line toilets, it's important that the discharge run up well above the waterline to a vented loop (siphon break), then down and out the thruhull. This is really important to ensure sea water can't siphon back through the toilets and flood the boat.


I had a similar issue and rather than tank venting, the issues was/is venting at the toilets themselves. When you flush it sends a slug of water down the hose. That will push air out ahead of it, which is dealt with by the tank vent. The moving water will also need to draw air behind it. If it's not properly vented, it will pull air through the water trap and gurgle. This is the problem I had. Tecma toilets are in my opinion defective in this regard, with a tiny vent with much too high an opening pressure, so air gets pulled through the trap water rather than through the vent valve. I'm only familiar with Techma toilets in this regard, but expect there is some venting provision in your Dometic toilets.



I think you said your thruhulls are below the waterline?

 

[HeadMistress]

...have you by chance come across a way to get them to automatically pre-fill with more water?

For most electric macerating toilets, the solution to that is to replace the single flush button with one that offers a couple of choices...bring water in and hold it, "dry" flush and the same simultaneous in/out as the single button. There are several brands, so pick one you like. If your toilet uses sea water the Raritan "Momentary Flush" won't work...only works on toilets designed to use pressurized fresh water.

--Peggie

 

[willd]

For your below water line toilets, it's important that the discharge run up well above the waterline to a vented loop (siphon break), then down and out the thruhull. This is really important to ensure sea water can't siphon back through the toilets and flood the boat.


I had a similar issue and rather than tank venting, the issues was/is venting at the toilets themselves. When you flush it sends a slug of water down the hose. That will push air out ahead of it, which is dealt with by the tank vent. The moving water will also need to draw air behind it. If it's not properly vented, it will pull air through the water trap and gurgle. This is the problem I had. Tecma toilets are in my opinion defective in this regard, with a tiny vent with much too high an opening pressure, so air gets pulled through the trap water rather than through the vent valve. I'm only familiar with Techma toilets in this regard, but expect there is some venting provision in your Dometic toilets.



I think you said your thruhulls are below the waterline?

Yes, my thruhulls are below the water line.

My toilet that is below the water line does run up above the water line to a vented loop above the water line, but it is only just above the water line. Is it necessary to be "well above the water line"? Also, I think that vent is usually screwed closed. Sound right?

That's interesting to know that Techma toilets have a (poorly desiged) vent valve in them. That sounds like it might be my problem as well. Maybe the vent valve on mine (if it exists) is either also poorly designed or old?

Will

 

[twistedtree]

Yes, my thruhulls are below the water line.



My toilet that is below the water line does run up above the water line to a vented loop above the water line, but it is only just above the water line. Is it necessary to be "well above the water line"? Also, I think that vent is usually screwed closed. Sound right?



That's interesting to know that Techma toilets have a (poorly desiged) vent valve in them. That sounds like it might be my problem as well. Maybe the vent valve on mine (if it exists) is either also poorly designed or old?



Will

The toilet installation manual should show the required height above the WL. I think it’s in the 18” range.

The cap on the siphon break isn’t a cap, it’s a one way valve. Most are a tiny rubber duckbill valve, and they need to be periodically cleaned and tested. Remove the cap and rubber duckbill, but be careful since they are easy to drop and lose. You should be able to blow in through the valve, and no water should come out when you flush.

 

[willd]

The toilet installation manual should show the required height above the WL. I think it’s in the 18” range.

The cap on the siphon break isn’t a cap, it’s a one way valve. Most are a tiny rubber duckbill valve, and they need to be periodically cleaned and tested. Remove the cap and rubber duckbill, but be careful since they are easy to drop and lose. You should be able to blow in through the valve, and no water should come out when you flush.

Thanks all.

I measured and my vented loop was close to the recommended height above the water line. All good there.

I ended up taking the toilet away from the wall and having a look. The 1.5" duckbill valve in the hose was old and not closing well, so I replaced that. I also wiped off the top of the valve where air can enter and made sure the rubber valve was allowing air in. It was. I'm not certain I did anything there, but maybe.

Whatever I did, it did not initially work. Kept bubbling. But after a week or so, the bubble went away. Not sure if it was replacing the duckbill valve or cleaning the air-intake vent. Either way, I'm bubble free, so no complaints.

Thanks all for the help.