Sunday, May 28, 2023


Can I swap my gravity toilet for a macerator toilet to help with dumping?

Dear Dave,
My fifth wheel has a typical Thetford gravity-style toilet, the kind that drops the stuff straight down to the tank. Are there any macerator toilets that would be a direct replacement? I am hoping to grind up the solids and paper before it enters the black tank. I am aware of the macerator options at the black tank drain but would like to make it easier for people renting my RV to drain the black tank. Thank you! —Craig, 2004 Keystone Sprinter 297BHS

Dear Craig,
Both Dometic and Thetford manufacture a macerating toilet that should fit in your RV. However, I question how it might make it easier to drain the black water tank?

What is a macerating toilet?

The traditional toilet as you mentioned is a gravity-style toilet that needs to be positioned either directly above the black tank or with a slight 45-degree angle. A macerating toilet grinds up the waste and pumps it to the black tank so the toilet can be placed just about anywhere in the rig. They have become more popular in floorplans that have a bath-and-a-half with a second toilet placed somewhere else in the rig, and the macerating toilet can pump the sewage to the black water holding tank. It also means a smaller drain pipe, as the typical gravity toilet uses a 3” pipe and the macerating can use a 2” pipe.

Here is the Dometic model, which you can purchase on Amazon here.

The Thetford model can be purchased here.

Some of the drawbacks of a macerating toilet are that they need 120-volt electricity and use a lot of water.

Will a macerating toilet make it easier to dump the black water tank?

Since your rig came standard with the gravity-style toilet, it is already plumbed with a 3” drain pipe that goes from the tank to the dump valve. If you use the proper toilet paper that will break down quickly and an aerobic tank treatment product that is enzyme based, it will break down the waste and toilet paper and should be no problem dumping the tank.

A macerating toilet will grind up the waste. However, it still sits in the same tank and you will still need to use a treatment product, otherwise you will get anaerobic digestion, which we call the “bad bugs” and the “rotten egg smell.”

Will a macerating toilet help prevent inaccurate monitor readings?

I would assume you are thinking that the macerating toilet will help prevent inaccurate monitor panel readings. However, I don’t believe it will, as the waste will still sit in the tank and can still cause inaccurate readings if you don’t use the proper products and properly dump the tank. I assume your rig has the probes going into the tank, like in the photo below.

Power comes to the single probe. As the fluid level rises, it creates continuity to the other probe and indicates 1/3, 2/3, and full. When you drain the tank, it is supposed to create an open circuit with no power going to the other probes. However, if the side of the tank has sludge or any other component, it will still provide power and a false reading. This can be lime, calcium, or anything else that would create a closed circuit and provide power and a false reading.

Using the proper treatment and toilet paper helps to digest the waste, and proper dumping procedures will ensure the tank gets cleaned. Typically, it takes 2-3 dumps and refills to get everything off the side of the tank. A black water flush valve is the best. If you are renting the rig, I would suggest using Tank Blaster by Thetford periodically, as most renters won’t take the time to properly dump the tanks—it’s typically a “one and done” dump! This will help clean the tank and reduce inaccurate monitor panel readings.

 You might also enjoy this

Not every RVer uses their RV’s toilet the same way… Wait, what?!

“I’m sorry. What did you say?” I thought at first that I’d misunderstood the statement. Up until then, I thought there was only one way to use the RV toilet. I quickly found out that I was mistaken! Turns out, there are two distinct groups of RVers when it comes to using the RV toilet. (At least two groups I’ve discovered. Who knows? There may be more!) Continue reading.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Jim Johnson
1 month ago

Dave, I know you mean a macerating toilet uses a lot of water in use and can fill the black tank faster than a gravity dump. But overall, I am doubting more water is used than what it takes to thoroughly flush a gravity fed tank. Please correct me if you have better information.

I use a flow meter on my black tank flush line. It allows me to close the gate valve and build water volume in the tank with minimal risk of overflowing. I find the total amount of flush water to clean the tank is 2X to 3X the capacity of the tank. That is a LOT of water! And certainly WAY more water than our residential toilet needs for comparable use. I am not talking about flushing until the sensors read E, but simply until no more waste is exiting the tank.

1 month ago
Reply to  Jim Johnson

We have a macerating toilet (Sanimarin) in the full bath of our motorhome. The half bath is a direct drop. I support Dave’s comment that it takes more water to get the same flush as gravity is not working for you. My best guess is it will take twice to three times the water to clear the bowl after a sit down #2. This is not my first go around with a macerating toilet as we had two of them in our sailboat. If we were swinging on the hook (anchored out) for more than three days we were looking for a pump out.

1 month ago
Reply to  Joe

I agree with you on the amount of water needed for a maceration toilet. Easily double the water as a direct drop and closer to triple wouldn’t be surprising. For dry camping I preferred our 40′ DP with direct drop to our 44 with 2 maceration units. All of our boats had vacuflush heads. I found the water usage on those to be similar to direct drop but have never seen a vacuflush in an RV. I’m not sure why not, hoping maybe Dave has a answer for that? On one boat we changed 2 direct drop on the boat to vacuflush with very little effort. One difference in boating was the gray dropped direct into the body of water you were boating on so our family and kids all learned young that organics and biodegradable products in the sinks and showers were mandatory.

Charlie Sullivan
1 month ago
Reply to  Jim Johnson

We have, and have used, our macerating toilet for the past 10 years. It does in fact use more water that a gravity flow toilet. However the ease of dumping and convenience of having a macerating system is worth the extra water. We do not boondock very often since we typically have to dump very 3 to 4 days…smaller RV, smaller black tank. After dumping the black tank, I open the grey tank valve and back fill the black tank with soapy water from the grey tank. Then close the grey tank valve, start the macerator pump and empty the black tank again, this time containing the soapy water. When empty, shut the black tank valve, open the grey tank valve and dump the grey tank while at the same time flushing the discharge hose.

1 month ago

I have a Dometic macerator toilet in our ‘22 Airstream, it is powered by 12V.

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