Cheap ways of detecting a PVC pipe underground ?

[CatalinaWOW]

I wouldn't worry too much about damaging the pipe with a pick or mattock.  The broad end of a mattock is extremely unlikely to do serious damage, and worst case the pointed end will make a small puncture.  It can be ignored, with the very real risk of future root penetration, or easily repaired with any number of materials.

Even if you precisely locate the pipe you will almost surely have to dig it up to clear the clog unless you buy or rent specialist equipment. 

If the risk and labor is daunting, perhaps hiring a pro to do the job is appropriate.

[tggzzz]

Fill it with oxy-acetylene....

As a kid I went to many lectures and demonstrations at the Royal Institution. One was a demonstration of the combustion of stoichiometric mixtures of several gasses with oxygen, culminating in acetylene+oxygen in a 1 pint glass milk bottle. Impressive, both on the eardrums and the multiple layers of protective devices around it. The milk bottle was nowhere to be found, but there was a heap of glass powder

Doubt they could do that nowadays

[JustMeHere]

Usually you can rent special purpose tools. 

Plan 2: find the tool on Ebay, buy it, use it, sell it on Ebay.

[fourfathom]

I wouldn't worry too much about damaging the pipe with a pick or mattock.  The broad end of a mattock is extremely unlikely to do serious damage

I don't know about that!  I've cracked many buried PVC water pipes, and sliced through numerous buried polyethylene irrigation lines with a mattock.  But a shovel is even more dangerous.

[Haenk]

One thing comes to mind: The company that installed these very same drainage pipes in my garden covered the pipes in coco fibre mats. The holes in the drainage pipes will let sand etc. get into the pipes, clogging them. The mats will block the particles and keep the pipes clean. Though being natural fibres, they do hardly rot, even if buried, and will probably outlast me.
So if you are redoing the piping, you might want to consider this.

[johansen]

I wouldn't worry too much about damaging the pipe with a pick or mattock.  The broad end of a mattock is extremely unlikely to do serious damage

I don't know about that!  I've cracked many buried PVC water pipes, and sliced through numerous buried polyethylene irrigation lines with a mattock.  But a shovel is even more dangerous.

I broke a 3/4" pvc schedule 40 water line with hardly a gentle touch. I knew the line was there, did not expect it to be only 8" deep in gravel.

A friend of mine says he can feel his backhoe touch a 3/4” pvc pipe. I think he is imagining things.

A 9cm pipe is 3.5 inches. At that diameter and thickness they are pretty tough.

[CatalinaWOW]

I wouldn't worry too much about damaging the pipe with a pick or mattock.  The broad end of a mattock is extremely unlikely to do serious damage

I don't know about that!  I've cracked many buried PVC water pipes, and sliced through numerous buried polyethylene irrigation lines with a mattock.  But a shovel is even more dangerous.

I broke a 3/4" pvc schedule 40 water line with hardly a gentle touch. I knew the line was there, did not expect it to be only 8" deep in gravel.

A friend of mine says he can feel his backhoe touch a 3/4” pvc pipe. I think he is imagining things.

A 9cm pipe is 3.5 inches. At that diameter and thickness they are pretty tough.

That has been my experience also. 

[Poroit]

G'day tigrou,

90mm pipe is normally Storm water pipe and it has thinner walls than Sewerage pipe.

I have experienced both these types of pipes being cracked/crushed by tree roots over a period of time.(Attached)

I assume this pipe connects to the guttering of your house to drain away rainwater.

Does the pipe empty into Drain or a Soak well?

I suggest you engage a Plumber who has an Inspection Camera to pinpont where the  blockage is and then you decide how to repair it.

If it has been underground for a long time it could be under some very big tree roots