Last Updated : November 20, 2020

Sun-Mar Excel Self-Contained Composting Toilet Review

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Living off of the grid doesn’t mean that you have to use a bucket or a pit as a toilet. Thankfully, there are composting toilets that don’t require electricity for regular use. This Sun-Mar Excel composting toilet is an excellent model that is the result of nearly 40 years of use and design changes. If necessary, you can use a solar panel to power a small 12-volt ventilation fan.

Product Overview

The Excel composting toilet first launched in 1981, and has been the go-to model for people who live off of the grid for years. Over the past 38 years, the model has been refined to include a lot of quality of life changes. One of these is the recessed drum handle that prevents hitting your shins when you’re walking around.

The Sun-Mar Excel does require venting and uses a 4-inch vent that exhausts from the rear of the unit. For best results, you should run the vent up to the roof and install it until it vents two to three feet above the peak. There is also a 1-inch drain in the rear of the toilet which should be diverted to an appropriate pit or disposal method.

Sun-Mar Excel Non-Electric

  • Uses no water
  • 100% non-polluting
  • Self-Contained Composting Toilet
  • Why we like it: The toilet is NSF/ANSI certified and can be used by up to 7 people depending on usage. Dimensions come out to 36x36x28 and it weighs in at 90 pounds even. 

This composting toilet is a little heavier, massing in at about 50 pounds, but that’s not so heavy that one person can’t manage. To open the drawer in front, you do require about 4-foot of clearance. It’s important that you do take measurements before installing to ensure that you can clean the toilet properly. But if you’re tired of using the outhouse and making that trek during the colder parts of the year, then this Excel composting toilet is definitely an option you should consider

How Does the Sun-Mar Work?

The Excel uses the Sun-Mar’s bio-drum design to compost waste in three stages. They are:

● Composting
● Evaporation
● Finishing

During the first stage, peat or coconut coir are mixed with human waste. After each use, the drum is turned, which aerates the mixture. This helps the aerobic bacteria in the mix break down the waste. This is done quickly so there’s no chance for odors to form.

The bio drum also helps to control the moisture content in the compost. As long as the moisture content stays between 40 and 60 percent, then composting will go on without trouble. As the bin is turned, moisture is distributed and the mix stays aerated and moist. Any excess liquid drains from the bottom through a screen.

Because the system is self-enclosed, the mixture is never exposed to direct sunlight or heat so the moisture and oxygen levels remain constant. The primary source of smell from compost happens when bacteria that don’t require oxygen start to flourish.

The Finishing drawer allows the compost to be finished without being contaminated by fresh waste. When you rotate the drum backwards, it will automatically place compost into the drawer. While it is in there, it is constantly dried until it is ready to be emptied and used.

Benefits of a Composting Toilet

You might wonder why you should use a composting toilet instead of digging an outhouse. There are several reasons.

● You prevent groundwater from pollution Human waste is about 90% water. Composting toilets evaporate this water and vent it to the atmosphere. The evaporated water doesn’t carry any pathogens so there’s no way for surrounding fresh water to be contaminated.
● Saving Water – Even with a high efficiency toilet, a family of four can go through 30 gallons of water per day flushing the toilet. A composting toilet prevents all that water from going to waste.
● Compost is good for your plants. You should never use traditionally composted human waste where it will touch edible plants. But that doesn’t mean that there aren’t other uses for it. You can use it as lawn fertilizer or to fertilize flowering plants. You can even use it on fruit trees. The oxidized salts that are in the compost are great for plants, and you will notice the difference right away.


● Compact and self-contained unit with a required footprint of 22-1/2 inches by 45-3/4 inches
● Installation is easy, using thinwall PVC as the vent stack.
● Does not require any electricity for use
● During sporadic winter use, can be used as a holding tank


● Uses a 1-inch drain that must drain to an approved location


As an alternative to a freezing outhouse or using a latrine trench, a composting toilet is a great idea. Whether you plan on using it for only a couple of weekends a year or you’re living fulltime off of the grid, the Sun-Mar Excel composting toilet is an excellent choice. But this isn’t the only option. If you’d like to see other composting or waterless toilet reviews, we have you covered with those too.

Charles Cole

Hello. My name is Charles. I have been in the home improvement industry for a number of years. One of the most important renovations that home owners can make is a bathroom upgrade. Not only does it add significant value to your home, but it also costs a fair amount to do. Bathroom renovations are not frequently undertaken so choosing your sanitaryware can be source of enjoyment or regret for years to come. This is definitely the case for toilets. Read more about me and the site here.

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