Plumbing - Compression Fittings
Male for going into floor drain
The following adapts from a male 5/8" compression thread to a 1/2" NPT thread female.
Anderson Metals 50066 Brass Compression Tube Fitting, 5/8" Tube OD x 1/2" Female Pipe
http://www.amazon.com/gp/product/B004QASNC2/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1 $6.34