Hi Mr Justin.  Not sure if ...

Hi Mr Justin.  Not sure if you are just wanting to control odour during the infrequent emptying operations of pits or septic tanks (lets assume this is carried out in about 1 hour per emptying operation), or whether the pits or septic tanks have ongoing odour problems.  Gary and Robert have given good comments below.  However I also wonder what the real issue is - we would normally expect some odours during emptying, but this is for a very short period for the household (e.g. 1 hour every 3 to 5 years) and can normally be tolerated.  If the workers are complaining, this is a different issue, and they should be provided with disposable face masks.  However if this is not acceptable, Gary's option of a lime-based product should be considered. In the case of ongoing odour problems from pits or septic tanks, I would concur with Robert that biological agents are more appropriate. In any event, try by all means to move away from chlorine compounds.