I assumed he had a carb like the ones in Sec 3 Page 20 of this manual. My assumption is then wrong and the diaphragm should then go against the tank. Sorry.
https://drive.google.com/file/d/0B6NaqjIxWV1ycG8wd0s3Z2Q2X00/view
https://drive.google.com/file/d/0B6NaqjIxWV1ycG8wd0s3Z2Q2X00/view