I'm putting in a hand basin for my son upstair bedroom, the nearest cold supply is just the other side of the stud wall in the loft area, is it okay to tee-off from the cold supply that goes to the F&E tank, it will be about 300mm below the tank, is it safe? I'm thinking if the chemical fumes in the F&E tank can draw back down to the hand basin, somehow I can't see how but want to play it safe.