Re' the wall....
It sounds like there is damp being absorbed either from the outside by the pipe itself (the pipe will be creating a "Cold Bridge" and allowing condensation to be absorbed into the bricks, or the pipe itslef still has a water feed to it behind the brickwork, which is leaking....
PVA will do nowt, as the damp is originating behind or underneath it, and will still bubble up.
Is the loo on the outside wall too?
This will 99% be condensation, and should be visible on the verticle bits of the cistern.
Is the bathroom/privvy heated sufficiently? If its chilly, then the condensation will be encouraged
Maybe look into getting the property surveyed for free by a local Green Deal Assessor.
They will make objective and impartial recommendations on "whole house" home energy efficiency, not just the particular issue you are asking about (be it insulation, a boiler, solar etc) and will provide you with a free report detailing energy savings, cost savings, and other things you havent already thought about