Blocked Bathroom Pipe - Caustic Soda?

Hi All
I have a bathroom with a bath, two sinks and a WC. When I run either sink for any length of time water starts coming up through the plug hole in the bath! Happily this does not happen when the WC is flushed - though the WC is immediately next to the soil downpipe and connects directly into it. Eventually the water which enters the bath does drain away.
My conclusion from this is that there is a partial blockage in the underfloor pipe which leads to the soil downpipe after the place where the closest (to the downpipe) sink joins that pipe. Thus water runs out of the sinks, hits the block and backs up into the bath (which is the path of least resistance as it is lower than the sinks). Having looked at the posts to this group, it seems that I should put a quantity of diluted caustic soda down the sink in question with a view to it disolving the blockage. Does that sound correct?
Many thanks for any help.
Chris
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On 21 Jan 2005 05:10:55 -0800, snipped-for-privacy@btclick.com (Chris Davies) wrote:

Maybe. Caustic soda is good on fats in kitchen sinks. For hairballs, conc. sulphuric acid drain cleaners may work better.
I've also recently seen, but not yet used, some US product that claimed to be an enzyme good at removing these partial slow-flow blockages. The caustics are good at a real "bung", but they may flow past something that's merely a narrowing.
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Handy tip. I'll try that if I ever start suffering from furballs. :)
Caustic is much more effective when used boiling hot, but its not safe stuff. One drop in an eye and youve really got problems, its worse than acid.
NT
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