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Hi @Barbara35,
All our drainage pits are listed on the Bunnings website. This Everhard Series 450 Stormwater Pit Case Only and Everhard Class A Galvanised Grate to Suit Series 450 Pit sounds like they'd suit.
Most stormwater pits are typically set into a bed of concrete to keep them secure and to prevent movement over time. Concreting in is recommended, especially in driveways, areas with vehicle traffic, or places with soft soil, to ensure stability.
The installation and connection of a stormwater pit would be considered plumbing and drainage work requiring a licensed plumber.
1.The prepared excavation should allow the Pit to be seated firmly on a layer of firmly compacted bedding
sand with the upper surface of the Steel Grate or Cast Iron Frame, whichever is selected, at the proposed
final surface level.
2. Mark and cut the Pit walls to accept the connection pipes or channels etc at the correct levels.
3. All pipes should be fitted through the Pit wall and sealed with a suitable silicone based adhesive/sealant.
4. It is normal practice to pour concrete inside the Pit up to the invert of the lowest pipe to prevent the
accumulation of water which encourages vermin to collect, and mosquitoes to breed.
5. The Grate should be fitted to ensure that the Pit walls do not distort during the completion of the paving
work. Internal bracing of larger Pits during backfilling is recommended.
6. Pour mass concrete at pipe entries outside the Pit walls to provide support to pipes entering the Pit walls.
7. Backfill the excavation with moderately compacted clean stabilised soil and sand.
8. Allow sufficient space above backfill for a concrete collar to be poured around the Pit, finished at the final
surface level. Collar depth and width should be the same, about 100mm for the Domestic Rainwater Pit
and 100 to 150mm for the Series 300 Pit. Collars should extend to not less than 150mm below the rim for
the Series 450, 600 and 900 Pits. This collar provides all-round support under the Pit rim for the Grate, and
protects the Pit against possible "in-service" mechanical damage to the edge of the rim. The diagram
overleaf indicates concrete surrounds in both light and heavy traffic sites.
9. Surrounding bitumen, concrete or brick paving should be planned for completion with graded areas so
that collected water flows towards the concrete collar surround and into the Pit.
Please let me know if you have any questions.
Mitchell
Hi @Barbara35,
I've updated my reply above with the full installation details from the manufacturer Everhard. Here are the installation instructions. The pit should sit on compacted sand material. 6. Pour mass concrete at pipe entries outside the Pit walls to provide support to pipes entering the Pit walls. 7. Backfill the excavation with moderately compacted clean stabilised soil and sand.
So, in the installation instructions, they require concrete to be poured around the base of the pit at the pipe connections. Regarding the lack of necessity for using concrete, I'm sorry, but I can only go by what is mentioned in the installation instructions. Due to your site specific installation, your plumber might have determined that concreting is not necessary.
I'm not familiar with orange plastic needing to be wrapped around the agiline, but I would suggest that a plumber would understand any regulatory requirements.
Mitchell
Afternoon @Barbara35
Just to add another opinion of the stormwater pits in gravel. I have several stormwater pits Everhard EasyDRAIN Polymer Rainwater Pit Case
Here is the links to my stormwater project
Stormwater rectification stage 1
Stormwater rectification stage 2
A few things to note espically things I would change -
- I sat the buckets on gravel, they are not tally level so I understand sitting them on a concrete base.
- They butted up too close to the foundation concrete so couldnt be next to the wall (yours does not sound like its next to a wall)
- The 100mm hole and the fitting. Yeah I screwed it on the outside of the boxs without silastic 
Its surrounded by gravel so not really fussed but if I am honest I intended to go back and silastic the joins and never did
- No reall movement since they have been burried, but you can tell one isnt totally level.
If you asked me to choose between the recomended install and the way i did it... I have generally found that there is a reason why its "recommended" 
For the layperson who does not do it frequently I try and stick to it. Then shake my head at myself when I work outside those rules.
Dave
Hello @Barbara35
In drainage, the difference between 15 mm and 20 mm blue metal (sometimes called aggregate or gravel) comes down mainly to particle size and the way water moves through it.
Fifteen-millimetre blue metal has slightly smaller stones, so the gaps between pieces are narrower. This means it still drains very freely compared to soil, but it holds a touch more moisture around the stones. It also compacts a little more easily, which can be useful under pavers or as a bedding layer, but for plant roots it can sometimes slow water movement slightly compared with a coarser grade.
Twenty-millimetre blue metal has larger stones, leaving wider voids between them. Water flows through more quickly with less resistance, and there’s less risk of fine particles clogging up the gaps. Because it is chunkier, it does not compact as tightly and generally provides superior long-term drainage, especially around soak wells, agi-pipes, or at the base of garden beds where you want water to escape fast. The trade-off is that it doesn’t “lock in” quite as neatly if you’re using it under surfaces, and it’s rougher to work with in small garden containers.
In short: 15 mm is fine for general garden use, topping, and bedding, while 20 mm is usually better where maximum drainage and void space are the priority.
If you have any other questions we can help with, please let us know.
Eric
