5/8" Siphon Vented Loop | Forespar 903003 FORESPAR 5/8" SIPHON VENTED LOOP 903003 Eliminates siphoning and backflow in marine toilet systems. Eliminates siphoning and backflow in toilet systems Install in between the discharge hose above the waterline, when head or holding tank is below the waterline Precision molded in high strength, lightweight Marelon so vent nor loop will corrode 5/8 in. hose barb size 4 1/2 in. height 4 in. width MF-843 model number