I just stumbled upon the PortaPura treatment plant  https://portapura.com/   It is aimed at the leisure market and the largest one they make is rated for 5 persons.  But it is a very compact treatment plant working on the air blower principle but in a totally different form factor.   At only 800mm deep for the 5 person unit it might be of interest to someone with difficult ground / bedrock?   I am not in any way related to this product, just mentioning it in case so