  We develop an abstract method to identify spectral points of definite type in
the spectrum of the operator $T_1\otimes I_2 + I_1\otimes T_2$. The method is
applicable in particular for non-self-adjoint waveguide type operators with
symmetries. Using the remarkable properties of the spectral points of definite
type, we obtain new results on realness of weakly coupled bound states and of
low lying essential spectrum in the $\mathcal{P}\mathcal{T}$-symmetric
waveguide. Moreover, we show that the pseudospectrum has a normal tame behavior
near the low lying essential spectrum and exclude the accumulation of non-real
eigenvalues to this part of the essential spectrum. The advantage of our
approach is particularly visible when the resolvent of the unperturbed operator
cannot be explicitly expressed and most of the mentioned spectral conclusions
are extremely hard to prove using direct methods.
