I just had week away with our SOG fitted and operational, WOW what a difference, absolutely no toilet smells, both chemical smells and the other smells are totally eliminated NO SMELL AT ALL, FANTASTIC.
Fitting was fairly simple, I followed the manufacturers instructions and also the very valuable tips of keeping the vent pipe long and higher than the tank to avoid siphoning and adding an extra screw to the switch bracket, tips from the kind folk on this site, thank you guys, it took me about 4 hours, the most time spent packing the access door with a block of timber to make it about 40mm thick.
I still use the chemical, however only need about half of what we used previously, so I guess over time the system will pay for itself.
For the past two years of daily use I have used only sodium percarbonate (Nappysan) in my caravan toilet, no smell, no issues, cheap, friendly to the environment and may be emptied into any toilet system.
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"I beseech you in the bowels of Christ think it possible you may be mistaken"
Oliver Cromwell, 3rd August 1650 - in a letter to the General Assembly of the Kirk of Scotland