Septic tank
While a properly maintained and located septic tank does not pose any more environmental problems than centralized municipal sewage treatment, certain problems can arise with septic tanks in unsuitable locations. Since septic systems require large drainfields, they are not suitable for densely built areas.
Bob Semple tank
The tanks were constructed without the use of any formal plans or blueprints. Working from an American postcard depicting the conversion of a tractor to a 'tractor-tank', Bob Semple and TG Beck (Christchurch District Works Engineer), improvised the design of the tanks. Using resources available to Bob Semple as Minister of Public Works, the first tank was quickly produced in the PWD's Temuka workshops. The additional two were built at the NZR Addington Workshops. The first cost £5,902; the second and third £4,323; total cost £10,225 (although the Army was only billed £3,414).