Relief pipe? ;-) But yes, I know what you are talking about.
Here it is — BLOAT TROCAR
Bloat Trocar Item # 17433
Wood handle trocar for relief of bloat when stomach tube will not relieve gas. Stainless steel 3/8” shaft has sharp triangular point for easy penetration of hide and rumen. Cannula provides opening through which the gas can escape.
17433 $17.29