Bath and Shower Sharing Waster Connection?

[Dermot Carroll]

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.

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.

Many thanks.

[mheden]

"...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..."

I have a similar situation relating to a bath and bidet. OK, the bidet outlet is a bit higher than that of a shower tray, but the bath water level is regularly way above that of the bidet outlet and I've never had a problem with bath water backfilling the bidet.

I should imagine that the key factors are the relative flow capacities of the bath outlet and the length of pipe that leaves your bathroom. Let's take an extreme example... If you had a bath and shower tray close together connected to a very long run of shared outlet pipe (such that the length affected the flow rate), then you might expect the bath to fill the shower tray unless you took steps to restrict the flow from the bath (such that it couldn't deliver more water than the long pipe run could cope with). In an even more extreme example imagine if the flow in the common part of the pipe is blocked. In that situation the bath water WILL flow back into the shower tray until it reaches a common level - something you obviously want to avoid. At the other extreme, imagine a bath and shower tray connected to a very short common pipe run... As that pipe run gets shorter and shorter, it has less and less effect on the flow. Eventually the flow rate is limited by the bath outlet and trap, at which point it becomes impossible for water to backfill the shower tray.

In my limited experience, provided that you use swept joints the right way round and the bath and shower don't share a long common length of pipe, and you don't encounter any blockages in the common part of the pipe run, there isn't a problem. If anything, I've found that the emptying of the bath creates suction at the bidet and sink such that there's a tendency for the water in their traps to be sucked out by the flow from the bath. Of course, although I haven't found this a problem in practice, this may be something you would want to avoid - and there's probably a regulation somewhere that relates to the effectiveness of traps and maybe even prohibits this sort of installation.

If you really don't want two separate drains I'd be inclined to test it. Tee into the existing pipe with a trap and outlet at the position where the shower tray is to be sited, fill up tha bath and see what happens.

Just my experience... and if you haven't already guessed, I'm not a plumber so you may want to disregard what I've said!

Mike

[bof]

In message , Dermot Carroll writes

It's not necessarily the case, my (large) basin and bath share a common outlet but the bath never fills when I pull the plug in the much higher basin. My washroom and kitchen also share a common pipe and the kitchen sink never fills from the washroom butler sink which about 2 or 3 feet higher than the kitchen sink.

I guess there are a number of factors which might affect whether the shower would fill or not, such as the relative lengths and drops of the pipes between the bath and tee, shower and tee, and tee and outside drop, and any vacuum generated by the down pipe. Of course if someone pulls the bath plug and the pipe is blocked/frozen beyond the tee then there's the potential for an almighty flood.

[auctions]

You shouldn't have a problem, but to be on the safe side, use a HepVo valve instead of a trap on the shower waste. It'll also prevent any gurgling or the bath pulling the water out of the shower trap. Available from plumbers merchants or from PlumbWorld I use them everywhere - they're great.

Andrew

[Dermot Carroll]

Thanks guys for your very helpful advice, it's very much appreciated.

I'll give it a try with the 'mocked up' installation as suggested by Mike and see how it goes. The longer run is from the bath, the shower will tee in relatively close to the ultimate connection to the soil stack.

If there is a problem, I can stick a stop end in the tee connector and get the SDS drill out!

Cheers, Dermot

[The Natural Philosopher]

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

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...