digraph Taskflow {
rankdir="LR";
#columns
subgraph{
p0[label="pipe-0 on item 4"];
p1[label="pipe-1 on item 4"];
p2[label="pipe-2 on item 4"];
p3[label="pipe-3 on item 4"];
px[label="pipe-3 on item 0",style="dashed"]
}

subgraph {
rank="same"
py[label="pipe-0 on item 3", style="dashed"]    
p0
}

p0 -> p1;
p1 -> p2;
p2 -> p3;
px -> p0;  
py -> p0;
}