my upstairs shower joins my downstairs wastepipe along with the washing machine waste. They seem to take it in turns to block! What is the best solution....chemical or otherwise to keep them clear? The only inspection drain is in my neighbours garden & we are at war over legal boundaries so I don't feel able to ask them about their drainage. Is there a weekly/ monthly proceedure I could follow to reduce the risk of future blockages? At the moment I am pouring sink & drain unblocker down the shower plug hole & leaving for the day....before flushing with hot water.....am I doing the right thing?
Im new to this forum but I am a qualified mechanical (air con and heating)design engineer and plumber.
First describe how you know they each take it in turns to block, does one branch back up then the other?
Next, describe how the waste pipes join (such as shower waste runs to outside at high level, falls vertical to join horizontal sink waste pipe running at low level, then runs to open gulley/discharges into soil stack/runs into ground and dissapears! etc)
There may be more than one issue (dont ever discount two separate (or more) faults causing an apparent single issue) and its a matter of working through a fault diagnostic question and answer process.
However I suspect from the description you have given that the fault may be a significantly but partially blocked run out pipe to the main sewer from your house. Now depending on what (probably trapped) gully you have that your waste pipe connects to at the back of your house, you could probably get a company to CCTV survey the pipe downstream then if blocked to carefully pressure wash the drain down to the connection with the main sewer.
The real answer, as I suspect you know, would be to lift the inspection chamber in your neighbours garden in the first instance, but you cant.