Dermot Carroll wrote:
Hi,

I am installing a separate shower in an existing bathroom. As the waste pipe
from the bath passes the shower location before exiting through the wall, it
would be a simple matter to 'Tee' into this for the shower tray.

However I assume that the shower tray would then start filling with water
every time the bath was emptied due to the higher level of water in the
bath.


You assume wrong, unless the waste pipe is blocked downstream..

Is there any sort of non-return valve that I could use in the connection
from the shower tray to make this work?

The bath and shower will not be in use at the same time so that won't pose a
problem. I would really like to avoid having to bring a second waste
connection through the outside wall.


I've done exactly this, and all I did was to make sure the shower had a
deeper trap than is sometimes used, and stands a bit higher than normal.
In practice the bath and shower water don't exit the drain holes fast
enough to build up a head, as they rush towards the bog with its 4 inch
vertical pipe ready to take the load..

IF that pipe were to be blocked, it would of course be a different matter...

Many thanks.