Will a 80mm rainwater pipe fit inside a 90mm rainwater pipe?

[Steve5]

I have an in-ground concrete water tank with 2 90mm overflow pipes that have now separated from the tank since the concrete slab on that side has moved - see photos.

The 90mm pipes are about 3m long buried in a sidewalk.

One gap is about 30mm and the other gap is about 15mm so I want to fill the gaps to keep snakes and toads out.

Ideas:

1.  cut section of PVC pipe to fit the gap and use sealant that works on damp/dirty surfaces.

2.  cut section of water bottle to fit the gap and use sealant.

3.  insert a 80mm PVC pipe thru the 90mm PVC pipe then into the concrete tank hole

Hence, the question whether a 80mm PVC pipe will fit inside a 90mm PVC pipe.

Any other ideas are appreciated too!

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[JacobZ]

Hi @Steve5,

Thank you for your question about reconnecting an overflow pipe to your rainwater tank.

An 80mm pipe will certainly fit inside the 90mm pipe, but it will not create a watertight connection.

I'd suggest grabbing 2 x 90mm PVC Stormwater Slip Couplings, a section of 90mm x 1m Stormwater Pipe, Protek Red Priming Fluid and Protek Type N Blue Cement Solvent.

Dig up around 300mm of the pipe and cut it back using a hacksaw then clean up the cut with some 80 Grit Sandpaper. Using the old cut off pipe, evaluate how deep into the rainwater tank it can be inserted. At least 150mm would be good if it is possible.

Once you've worked out how deep into the overflow outlet you can get a pipe, cut a section from the 1m length of 90mm pipe that is long enough to insert into the overflow and bridge the gap to the old pipe. Make sure to clean up the cut end with the sandpaper to ensure good adhesion. 

Apply the red priming fluid to the outside of the pipe and the inside of the slip coupling. Allow the primer to dry for 30 seconds or so before applying the blue cement solvent to both the pipe and the slip coupling. 

Fit the slip coupling over the end of the pipe and rotate it 90 degrees to create suction between the two masses of solvent. 

Once the slip coupling is in place, insert the other end of the pipe into the overflow outlet and repeat the priming and gluing process on the other side of the slip coupling to glue it to the old 90mm pipe, ensuring to rotate it 90 degrees to create suction between the adhesives.

Repeat the process with the other outlet and then bury them to conceal the pipes. This will give you a strong and watertight repair.

Let me know if you have any other questions.

Jacob

[Steve5]

Hi Jacob,

Thanks for the response and extensive details but I want to avoid breaking up the concrete.

Good to know the 80mm will fit into the 90mm as that will allow me push pipe thru the 90mm into the tank.

I'll seal the best possible with limited access and then cover that section with concrete.

[JacobZ]

Hi @Steve5,

Apologies, I missed the fact that there was concrete on the right side of your images. 

Regardless, you're going to have to cut the pipe back at least a little bit in order to slip the 80mm pipe into the 90mm pipe.

 I've tested this in store and can say that it is a very tight fit, so if you are struggling to get the 80mm pipe into the 90mm pipe, run a relief cut vertically along the pipe. See the below image as an example of what I mean. 

This will allow that little bit of extra play that you might need to slot it inside the 90mm pipe. You should still use the red primer and blue solvent cement to fix it in place, but you might want to run some Sikaflex 11FC around the outside of the connection to give it an extra seal.

Let me know how you go.

Jacob

[Steve5]

Thanks for followup.

Is relief cut only needed to get the 80 started inside the 90?

Previously, I used an angle grinder to cut out a strip on a PVC pipe to create a slot so it would slide over a folding dog gate to keep it straight.

For this project, I thought about making a cut down the length of 80mm pvc if needs compression to fit in 90mm pvc.

This time, I might clamp on folding work benches with a 70x34 pine to create a guide for my circular saw.

Thoughts?

[JacobZ]

Hi @Steve5,

The relief cut is only needed if you find that it is too tight to slot in. It will allow the pipe to fold in on itself that little bit to slot in nicely, while still remaining tight. I'd suggest the relief cut only needs to be as long as the section that will be inserted into the 90mm pipe and the cut is on the top of the pipe when it is inserted. Anything beyond that is just creating an unnecessary gap in the pipe where water can leak out.

Either the angle grinder or the circular saw will work, but whatever you choose to do, please prepare accordingly. 

Take all necessary steps to make what you are doing as safe as possible and wear the relevant personal protective equipment including eye protection, hearing protection, gloves and a long-sleeved work shirt.

Let me know if you have any further questions.

Jacob