For instance, hot tubs and {HEAD ~ swimming pools} often maintain {TAIL ~ a constant circulation} of water through a filter and heater assembly to clean and heat the water passing there through 
For instance , hot tubs and { HEAD ~ swimming pools } often maintain { TAIL ~ a constant circulation } of water through a filter and heater assembly to clean and heat the water passing there through
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH 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