A multicast routing network is obtained from a general communications network where the source nodes and sinks are specified. We propose a method that generates an approximate multicast routing graph, in which the scheme of simultaneous transmission and reception of packets using Network Coding can be checked. The proposal is based on the maximum flow algorithm, developed by Edmonds-Karp, which determines the individual maximum flow graph for each sourcesink pair. A debugging is carried out to determine the minimum flow between the set of individual solutions, and then the resulting graphs are mixed to establish the minimum common flow graph of a single session multicast routing system. A Network Coding scheme has a solution over the multicast graph, if and only if, the packets sent simultaneously from the source node can be recovered from a system of linear combinations that enter the sink nodes.