In this work we present the experimental verification of different approaches to calculate the rate of the outgassing of cometary analogues. We investigated both new, and known formulations applicable for the mass flux of water vapor from mixtures of ice agglomerates. For the purpose of the verification we performed experiments using samples composed of different ice agglomerates. We tested both samples made of approximately uniform agglomerates and samples composed of agglomerates of hierarchical structure. The largest agglomerates have diameters about one centimeter. All experiments were performed in vacuum. We have found, that at the temperature above 200 K the pressure of vapor between agglomerates is close to the pressure of the phase equilibrium and exhibits some dependence on the temperature. We propose the appropriate functions. In addition, we present the method of calculating the lifetime of large centimeter sized porous ice–dust particles present in cometary comae.