Sorry I meant soak away not Tank. I did presume that we are talking about a soak away, and not a tank. I have owned an old property in the UK that had a soak away and was never a problem. Design, sizing and installation are important, of course, if all these are adhered to and the soak away is not abused, there is little to no maintenance required. This of course may not be the case in this particular installation. Only trying to be helpful!