- The biotank is designed for domestic sewage, it uses natural biological bacteria in both aerobic and anaerobic chambers of the tank to digest sewage into nitrate's, nitrite's and other biodegradable compounds. Effluent can be discharged directly to a watercourse without the need for a soakaway. The biotank is superior in its treatment of organic waste to biocycle, klargester, biodisk, bioclere, ...biotank.co.uk