Not doubting you in the slightest, but your time between dumps of the cassettes is a bit shorter than mine. Again 2 people, 20l / 5 gallon portable toilet in my case needs to be emptied for us every 4 to 5 days when out. Of course i have no qualms just watering the bushes if need be instead of using the toilet. my wife on the other hand is not comfortable with that...View attachment 681087
We use a cassette toilet. We spend a lot of time in the desert and usually need to bury the contents.
This hole will accommodate both ours and our friend's 20L cassettes.
Cassettes typically need emptying every 3 or 4 days when used by 2 people full time. But, if ALL urine is diverted and flushing water is minimised, a cassette can last up to 2 weeks for 2 people. It also smells a lot less.
We have had one trip with uh... some digestive issues that came up and dumping was needed at 2 days, but that is a completely different story... At that time, I was happy to pack up and go home. I got a bad burger at Fuddruckers en route. Not even sure if they are still in business.
FWIW, how deep do you dig your trench? I tend to go at least 24". They used to say to keep it at that depth so it decomposes fastest and is away from the ability of moth animals to get to it...