Digests 124 and 125 suggested considerable modifications in current practice in the design and construction of drains and sewers in this country and as a result a number of comments were received from the National Federation of Building Trades Employers. A meeting was therefore arranged between members of the Federation’s Building Research and Technical Information Committee and the Building Research Station to discuss these comments fully and it was agreed, in view of the importance of the matter, that the Station should issue a further Digest based on the discussion. This Digest presents the results of the meeting in the form of a series of questions and answers.