K4-R O'RING, WATER FILTER TANK | OMNIFilter's K4 undersink drinking water O-ring kit is for use with OMNIFilter filter housings OT32, CBF1, CBF3, USM3, SFM2, OCT2, RO2000 and RO2050. Kit contains 4 different sized O-rings and silicone lubricant.