A house with no mains sewer needs its own system: a septic tank with a soakaway, or a compact treatment plant (depuradora) that cleans the water further. Which one suits depends on the plot, the soil and the local rules.
Ask the firm what the soil can absorb, where the tank can go and how a lorry will reach it for emptying. A treatment plant costs more and needs power, but the water it discharges is much cleaner.
Every system needs emptying from time to time; how often depends on the size of the tank and the household. Firms that fit tanks often empty them too.
Questions to ask before you sign
- Septic tank or treatment plant: which suits my plot, and why?
- Has the soil been tested?
- What does the price include, from digging to commissioning?
- How often will it need emptying, and do you do that?