PlanesPete wrote on Jun 12^th, 2016 at 7:33am:

It is not usual to empty a concrete, traditional, septic. It's important to keep natural bacterial processes going to dissolve the waste. You can buy sachets of bacteria to flush down the toilet. Look for WC-Net in many supermarkets. Also avoid putting bleach down as it kills the bacteria.

Thanks, it's what I though. We do use the sachets.

Following on from the bleach comment, if I'm refreshing my cisterna with bleach, will that be an issue?