x1=t1 is a pipe/tube/hose carrying fluid x2=f2=t3 towards x3=f3 from x4=f4 (direction/source)
Fluid is any flowable matter (gas, liquid, slurry, powder etc.). Cf. jaurflevau, datnyfle, blutu'u, tubnu, pambe, litki, gapci, bumru, danmo, purmo, pulce, sligu.