Walk in shower sealing

[craftor]

hi
I'm thinking of building a walk in shower which is downstairs with an existing cement screeded floor. I'll have to break up some of the screed to fit a lower waste to a small plastic tank buried below the screed and but I'll have to breach the pvc membrane
Any thoughts on how to repair the membrane. Cheers

 

[Newboy]

What are you planing to install below floor level? (tank/pump etc?)

 

[craftor]

Yes, I plan to build a screeded/tiled shower area,the drain will be lower than the existing floor level then tapered outwards for the correct fall. There is a tank already present as there wasn't a direct route from the toilet to the back drop manhole so I'll feed into that
There is an existing shower present which is built on a wood plinth, the waste is above floor level