Multiple 'layer' parameters can be sent by simply putting a comma between them: 'layer=low,extra' or layer=low,water,meta'. This results in all of the segments requested being returned in the same line, so you would first split them by a tilde. The first element of each segment is the layer_code, so inspecting the first two characters will tell you which segment you're working with. Splitting each of these segments by an asterisk will get each of the elements.
NOTE: the order in which the layer strings occur does not affect the output order. 'layer=low,meta' will have the same result as 'layer=meta,low'. The output order is always: Header, Meta, Low, High, Extra, Water
hd*ParfaitAPI*https://api-parfait.omegatower.com/*current****KLAX**head,low,high,extra,water,meta*20160213*1239*2601:140:8202:cd8f:d9f9:8824:128e:eb05*2016.02.12.17~mt*NOAA's National Weather Service*http://weather.gov/*15 minutes after the hour*60***http://www.weather.gov/data/obhistory/KLAX.html*http://www.weather.gov/data/METAR/KLAX.1.txt*http://weather.gov/disclaimer.html*http://weather.gov/disclaimer.html*http://weather.gov/notice.html~lo*KLAX*Sat, 13 Feb 2016 08:53:00 -0800*Patches Fog*58.0*14.4*93*0*0.0*0*55.9*13.3*****6.00*~hi*Los Angeles, Los Angeles International Airport, CA*Last Updated on Feb 13 2016, 8:53 am PST*Patches Fog*58.0 F (14.4 C)*93*Calm*55.9 F (13.3 C)***6.00*~ex*33.93806*-118.38889****1019.4 mb*1019.4*30.11**~wa**************~