Waste Water Management

My wife is building a new house. Although directly adjacent to a road along which are many 'houses' there is no municipal drain (sewer) into which to connect waste water from the house and septic tank outflow.

She intends to build a 'soakaway' a cement block bottomless tank with concrete roof with manhole cover. The resultant box to be partly filled with aggregate (gravel). An overflow pipe would be installed into the top of the 'tank'

The Tessabahn approved plans show a circular concrete cylinder about 1m in diameter buried flush in the ground. The pipe is perforated and the void on outer circumference of the tank is filled with aggregate but there is no overflow and the 'tank' bottom is sealed.

Can anyone offer advice on which type of 'soakaway' would be better. It will need to take the daily waste water from the house (1 bath two showers and kitchen plus the outage from two 1600 septic tanks. Should there be an overflow pipe in case the 'tank' gets full.

The house is well off the ground by two metres so there is plenty of fall for the waste pipes to tank.

The municipality say that a main drain is scheduled to go into the roadway this year.

Anyone constructive advice will be welcomed.