The Double VIP has almost the same design as the Single VIP (S3) with the added advantage of a second pit that allows the technology to be used continuously and allows for safer and easier emptying. By using two pits, one pit can be used while the contents of the second pit rests, drains, reduces in volume, and degrades. When the second pit is almost full (the excreta is 50cm from the top of the pit), it is covered, and the contents of the first pit are removed. Due to the extended resting time (at least 1 year of filling/resting) the material within the pit should be sanitized and humus-like.
None of the options were relevant for Double ventilated improved pit.