  We perform a SU(3) analysis for both semi-leptonic and non-leptonic heavy
meson weak decays into a pseudoscalar meson and a fully-light tetraquark in 10
or 27 representation. A reduction of the SU(3) representation tensor for the
fully-light tetraquarks is produced and all the flavor components for each
representation tensor are listed. The decay channels we analysis include $B/D
\to U/T~P~l\nu$, $B/D \to U/T~P $ and $B_c \to U/T~P/D$, with $U/T$ represents
a fully-light tetraquark in 10 or 27 representation and $P$ is a pseudoscalar
meson. Finally, among these results we list all the golden decay channels which
are expected to have more possibilities to be observed in experiments.
