Construct two pipes joined as thus:

> restart;

> x:=cos(t):

> y:=sin(t):

> z1:=-1.5:

> z2:=x:

> z:=(1-s)*z1+s*z2:

> a:=plot3d([x,y,z],s=0..1,t=Pi/2..3*Pi/2,scaling=constrained):

> with(plots):

Warning, the name changecoords has been redefined

> with(plottools):

> b:=reflect(a,[[0,0,0],[0,0,1],[0,1,2]]):

> c:=display(a,b):

> d:=rotate(c,0,Pi/2,0):

> e:=rotate(c,0,Pi,0):

> f:=rotate(c,0,3*Pi/2,0):

> display(c,d,e,f);

>