Saturday, September 9, 2017

Replacing That Smelly Toilet Bowl in a Roadtrek Agile

My 2011 Agile came with a Thetford Aqua Magic V toilet which I've replaced twice with same model due to holding tank fume leakage around the flush valve assembly. The last replacement lasted about 2 years of use then it started to leak fumes again! 
Thetford Aqua Magic V design is not very well thought-out IMHO; the space between the toilet bowl and the toilet outer casing/base is hollow and open to the black tank. Waste splatter can get stuck in that hollow space during flushing, very unhygienic. The flusher arm seal is also unreliable, it is basically sealed with packed grease. When grease seal starts to dry up, it starts to leak fumes from the holding tank especially when there is negative pressure inside the van like driving with windows open.
Here is my old Thetford toilet cut open in half so you can see the innards. Take note of the cavernous inside with no access for cleaning, all waste splatters in that area will be stuck there and possibly contribute to a very smelly toilet.

Looking up from the bottom of the Aqua Magic V, see the hollow inside (green arrow pointing).
Here is the flushing arm seal, the black foam seal is there just to hold the packed grease in place.
The black gasket is made of soft porous foam.

The grease seal is starting to dry up in this 2 year old toilet. I did a water pressure test before taking the toilet apart and sure enough water just comes pouring out around the flusher arm seal.
To better illustrate Aqua-Magic V design flaws, I added toilet cut-out illustrations below:
Take note of the huge open space (light brown color in illustration) between the bowl inner wall and the outer wall casing, this space is fully open to the black tank underneath.

When flushing the toilet (either via foot pedal or hand flush depending on model) the flusher arm swings out allowing water and waste to drain by gravity, the outer wall acts as a funnel to direct water and waste into the holding tank, unfortunately some solid waste can splatter and can get stuck into the outer wall.

NOTE: If you’re noticing bad smell emanating from the bathroom area and just cannot figure out where it is coming from, do a water leak test on the toilet to see to see if it’s airtight. 

To do the water leak test you have to remove the toilet bowl from the pedestal, undo the two floor holding bolts and the water line towards the back of the toilet. Once removed, put the toilet upside down and fill the cavity with water up to the brim, see if there are leaks. If no leaks, then your toilet is good and the bad smell is coming from somewhere else
Next is finding a suitable toilet replacement that will fit the Roadtrek Agile tiny wet bath.
 Roadtrek Agile toilet flange distance to bathroom back wall is very limited measuring about 8.5 inches from the flange mid-center to wall. Most RV/ Marine toilets needed at least 9.5 inches or more to fit.
Dometic 300 Series Low Profile toilet is the ticket, it is listed that it only needs 8.5" clearance to fit. The toilet water inlet is the outermost part of the toilet and it sits closest to the wall when installed; you need to install a 90-degree elbow at the water inlet for the toilet to fit.
A side by side size comparison of Dometic 300 Series and the Thetford Aqua Magic V toilets. The Dometic toilet is slightly wider (about 7/8" wider) and sits taller (about 0.75" taller) than the Thetford.
The factory water line fitting was replaced with a 1/2 inch barb to 1/2 inch male NPT 90-degree elbow fitting. I use a foot long 1/2 inch FIP x 1/2 inch FIP water supply flexible hose to connect the toilet to the water line.
With the 90-degree elbow and supply hose connected. Take note of the supply hose connector fitting which is almost touching the back wall in the above picture, that is how tight the clearances in the Agiles' small bathroom. The toilet bowl uppermost part has about 0.5" clearance from the wall.
  NOTE: The new Dometic toilet is slightly wider and needed to be installed slightly facing inward to prevent the toilet lid from making contact when opening to the left inverse corner of the bathroom wall. 

 The flush pedal of the Dometic toilet slightly interferes with the new set of toilet paper placement, but...I did not find it to be a problem. I added an anti-skid tape cut to size to top of the pedal flusher.
Some Pros and Cons of Dometic 300 Series toilet over Thetford Aqua Magic V
  • Better seal and flush operator assembly design.
  • The hollow space between the bowl and the outer casing/base is sealed and not open to the black tank.
  • Toilet seat and lid remains upright and vertical against wall when opened preventing unnecessary closing during use. Thetford lid and seat is hinged further back and because of the back wall clearance, they are not fully vertical when opened.
  • Easy serviceability, worn out parts except the flange seal can be replaced without removing the toilet. 
  • Slightly wider and taller and takes a little more bathroom space.
  • The plastic seat and base makes a slight creaking sound when seating on it, can be annoying to some.
  • Slightly tricky to flush with the bathroom door closed due to placement of the foot flusher, not a deal breaker IMHO.


  1. For an even more scathing review of the Thetford Aqua Magic V, readers can see our very similar toilet replacement project at this link below. I sure wish there were better quality options for those of us with tiny wet bath spaces, but such options do not appear to exist at this point in time.

    1. It is hard to really visualize the problem with the toilet design so I added toilet cut-out illustrations to better illustrate Aqua-Magic V design flaws. No wonder Thetford recently shorten the toilet warranty from 3 years to 1 year, I wonder how many RVer's having the same problem with this toilet.

  2. Just bought a new APEX trailer this year and first trip out experiencing the same flaws. I was wondering if the forgot to install an internal part of the toilet. but I guess it is just bad design.

  3. Would you recommend the Dometic 300?

    1. I'll recommend the Dometic 300 over the Thetford Aqua Magic V. There are many better quality RV toilets in the market, the porcelain ones are nice, but none would fit my Agile (see above post).


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