What agi & PVC pipes are best for stormwater pipe connections?

joey77

Hi there!

I've got a few questions about stormwater pipes (agi and PVC) and the correct connections for them. I've had a look around the forums but couldn't quite find what I was looking for. Any help would be amazing!

General questions

• are DWV (Drain Waste Vent) pipes best for underground purposes? I noticed some similar looking products have very different prices and presumably are for different purposes? For example, compare 90mm PVC Junction ($3.15) with 100mm PVC DWV Junction ($10.65)
• are underground PVC pipes usually 100mm? Again, similar looking products but some are 90mm diameter.
• I noticed some of the tee and Y junctions have threaded ends -- are these just for caps, like an inspection point? See the above links for examples. 
• I noticed some of the L-shape bends are 88 degrees not 90 -- why is this? Do you still refer to these as 90-degree bends? Is it just to help water flow out of the bend easily?

Project-specific question

I am constructing a concrete block retaining wall with a concrete footing. The wall needs a 100mm agi pipe behind it and I would like to know how best to connect this to the stormwater pit.

I was initially going to connect the agi pipe straight to the pit like in the photo below, but this is going to be difficult to concrete around because the agi pipe is so flexible. That got me thinking I should use a rigid PVC connection instead. Please see my sketch below for what I'm now thinking.

Please note: there are two (2) agi pipes in the sketch below. One connects at Point (2) going into the screen / page. The other comes from the top of the embankment which serves other parts of the garden and I'm proposing to connect at Point (4).

I am proposing to install 100mm PVC DWV pipes and 100mm agi pipes and connect them with the following products (numbered per the image below)

• (1) = Holman 100mm 88° F-F PVC DWV Plain Bend 
• (2) = Holman 100mm 45° Female And Female PVC DWV Plain Junction
• (3) = same as (1)
• (4) = Vinidex 100 x 100mm PVC Draincoil Adaptor

Would this work? Is it the right way to connect these pipes together? What would you do? Interested to hear your thoughts 🙂

Cross section view of the proposed retaining wall i.e. looking from the side. Total length of wall is approx. 15m long

Photo of where I'll be building the retaining wall

EricL

Hello @joey77 

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about stormwater connections.

Allow me to try and answer some of your questions.

• DWV are designed for underground use. You'll notice the difference between the 90mm PVC Junction and the 100mm PVC DWV Junction. The 100mm junction has thicker walls which means more material was used in manufacturing this junction making it much stronger than the 90mm junction.
   
• It all depends on the needs of the plan and project. Sometimes it's not necessary to use 100mm and a 90mm pipe will suffice.
   
• The "T" and "Y" junctions all do double duty even if they have threaded ends. They are able to accept pipe work at the bell ends and they can be used as inspection junctions and capped off.   
   
•  All '90 degree' angled fittings are traditionally noted as "90 degree" but are, in fact, manufactured at 88 degrees, this is to allow for drainage purposes.

In regards to your project specific questions, I suggest engaging the services of a licensed plumber. They will be familiar with the rules and regulations regarding your plumbing project. Council regulations also require that a plumber links your drain into the stormwater system.

I propose showing your plans to the plumber and getting their opinion. They'll be able to tell you if it needs more pipework and if it will work properly.

If you need further assistance, please let me know.

Eric