iv got some bicarb in cupboard how much do you mix with water https://www.nhs.uk/conditions/non-allergic-rhinitis/treatment/To make the solution at home, mix a teaspoon of salt and a teaspoon of bicarbonate of soda into a pint of boiled water that's been left to cool to around body temperature (do not attempt to rinse your nose while the water is still hot).
The instructions say to put some in your hand and suck it up - sounds like it will go up in surprising spurts. I usually use a tall thin glass and try and suck some up one nostril until it reaches the other end (learn this is stages), then blow it out. If it is the right temperature it is not too noticeable until you have to stop.
Have an old towel handy for the fall out.
When I am more civilised, I use the spray stuff from the Chemist and tissues. It is a bit expensive but a special treat for the hayfever season
