That was the problem facing me earlier today. Needed to replace a 15mm
pipe coming off a tee. Problem was that it was below the lowest drain
point on the water circuit, so I knew the pipe had water in it that
would most likely cause problems when applying a blowtorch.
Solved the problem after sleeping on it overnight. I'm passing the
following on in case it might be useful to someone else one of these
I drained the pipework as far as I could, leaving a few feet of 15mm
containing water - with the tee midway along.
Then connected up my Acquvac vacuum cleaner configured in wet mode,
stuck the hose on the tap on the end of the circuit, opened the tap at
the other end of the pipework, and sucked the water out.
Within a couple of minutes I had nearly-dry pipework which allowed me
to break and remake the 15mm solder tee without problems.
I suppose a complete job would have seen me put a drain valve on this
pipework for good measure. Didn't bother - now that I know my trusty
Aquavac can do the business I don't need the drain valve :)