When the s**t hits the fan.....

Our trailer is very well equipped with shower, central heating, air conditioning etc.  The waste system is quite up to date as well involving 3 waste water storage tanks, one for kitchen waste, one for bathroom waste and another for the toilet. Now, the two "grey" water tanks feed directly into the sewage system via an airtight connection to the septic tank. The "black" water, (poo etc) is held in the tank and is released weekly which involves flushing the tank with a sanitiser once dumped. 

Last week I forgot the scheduled dump so the "black" water tank filled to capacity and the overflow outlet made itself known to me. Luckily the outside air temperature is very low so there was no smell under the trailer however we did grow a slightly odd coloured stalactite, os is it a stalagmite?