Ventilation Pipe Flooded Loft

Our house is about 20 years old and this is the top of the toilet vent stack where it goes through the roof. I had the misfortune to knock this pipe this evening and 20 years of condensation released itself from the low point of the curve. I'm not sure what the builders were thinking as this is only held in place with a push fit and so it seems inevitable that it would eventually fill up with condensation and the fitting wouldn't be able to take all that weight.



I have cut out the damp insualation and put a dehumidifier in place to dry the remaining damp. What is my best option for a permanent fix for this vent?
1) Cut back the grey pipe and use the flexible section to connect to the roof vent without the u-bend?
2) Cut back the grey pipe and install an air admittance valve (Durgo) on the end of it?
3) Another option I haven't thought of?

Thanks in advance for any advice you can give me.

option (1)
Any dip in the flexible will collect condensate (vaporised shyte)

slangivar said:

I'm not sure what the builders were thinking

Click to expand...

Not all builders actually have the ability to think, ( other than what time the pubs open ).

If possible shorten the grey pipe so the the black flexible pipe has a straight run from grey pipe to roof outlet.

There will the condensation forming in the pipe and this may now, instead of being collected in the U bend, run down the inside of the grey pipe. Lagging the gey pipe and the black pipe will reduce the amount of condensation.

Thanks for the advice. I managed to wedge the pipe away from the wall and shorten it. I also turned the flexible pipe round so that any condensation will be fed inside the lower section. The top seal was fairly weak so I added some string to stop it vibrating loose. It now looks like this:



I then checked and found the setup repeated further down the loft but the grey pipe wont move so I have ordered a flexible saw to cut it. In the meantime I drained the u-bend.