Q.Root systems
How aggressive is the root growth of a Hibiscus plant? Can it be safely planted next to a wall or close to a sewage line?

Tropical Hibiscus are hardy in zones 9 and above.
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm
Hibiscus do not have an aggressive root system.
Here are some articles that have planting information for you.
https://www.gardeningknowhow.com/ornamental/shrubs/shgen/foundation-plants.htm
http://www.extension.umn.edu/garden/yard-garden/landscaping/landscaping-septic-systems/