i believe stack/drain connections should always be installed in the horizontal plane

IMO connection via "Y" or "T" on its back is poor trade practice as solids will clump/lump at this point in drain unless ALOT of flushing water is discharged at the same time thereby being prone to blockage at this point

using a 90 in the vert to head down with 2x45's into a "y" on the flat/horizontal maintains a best possible consistent flow and will therefore be less prone to blockage


may not matter so much on a single or even double storey residential property but once you start getting into multi's this becomes much more critical

Also thinking on how the waste/air moves within the pipe...if you drop in from above and the upstream section of drain is also in use then you have the possibility of interupting the flow of air and waste within the system where as side entry will allow air and waste to move and combine more freely within the two systems...at a guess.

And also i think they draw it like this as the main drain never huggs the side of the building and you have to double 45/or radius bend at base of stack to get out to main drain anyways as drains have to be a certian distance out from a building and drainage connections have to be swept anyways...

Ha ha a little more digging came up with this info...

In the g13 drainage section look at...

3.2 Junctions
3.2.1 Any connection to a drain, excluding vent
pipe connections, shall be made by means of
sweep or oblique junctions. The angle that the
branch makes at the point of entry with the
main drain, shall be no greater than 60° (see
Figure 1). it shows a horisontal connection and also a vertical connection so this option seems to be allowed.

Also for further explantation as to why G13 AS1 Fig 8 is drawn in such a manner...
5.6 Proximity of trench to building
5.6.1 For light timber framed and concrete
masonry buildings founded on good ground
and constructed in accordance with NZS 3604
or NZS 4229, pipe trenches which are open
for no longer than 48 hours shall be located no
closer than V to the underside of any building
foundation, as shown in Figure 8. Where the
trench is to remain open for periods longer
than 48 hours the minimum horizontal
separation shall increase to 3V in all ground
except rock.
Also look at Figure 8: Relationship of pipe trench to
building foundation.

But i still think dropping in from a vertical position is a last option BUT it is still an acceptiable one.

hope that helped. 

Np happy to help sir, as you learn i also learn lol thats REAL CPD at work! and it was free!

I've put all three rodding points at the web location posted above. The first is near the head of the drain, where it originates at a shed. The second where the drain enters under the house. The third where it exits from under the house, and is joined with the graded discharge pipe from the house, and continues to the septic tank.

Any comments on the drain layout would be appreciated, specifically with respect to that third rodding point/junction. Thanks.