{HEAD ~ The reservoir} is preferably {TAIL ~ a replaceable unit} which is available commercially and which is fitted with a removeable cap to adapt it to the system 
is preferably
{ HEAD ~ The reservoir } is preferably { TAIL ~ a replaceable unit } which is available commercially and which is fitted with a removeable cap to adapt it to the system
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH