\documentclass{article}
\usepackage{gastex}

\begin{document}

% offsets

\begin{center}
\begin{picture}(60,50)(0,0)
  \put(10,10){\unitlength=1.2mm
    \gasset{Nmr=0,Nfill=y,fillgray=0}
    \node[Nw= 1,Nh=10](B)(0,20){}
    \node[Nw= 1,Nh=10](C)(30,20){}
    \node[Nw=10,Nh= 1](D)(15,0){}
    \drawedge[syo=3,eyo=3,curvedepth=3](B,C){}
    \drawedge[syo=1,eyo=1](B,C){}
    \drawedge[syo=-1,eyo=-1](C,B){}
    \drawbpedge[syo=4,eyo=4](B,165,30,C,15,30){}
    \drawbpedge[syo=-3,exo=-3](B,0,10,D,90,10){}
    \drawbpedge[syo=-3](C,180,10,D,90,10){}
    \drawbpedge[sxo=3,eyo=-5](D,90,10,C,-90,10){}
    \drawloop[sxo=-3,loopdiam=4,loopangle=-90](D){}
    \drawloop[sxo= 3,loopdiam=4,loopangle=-90](D){}
  }
\end{picture}
\end{center}

\end{document}