To be part of a church, one must be a member of that church. One also must be regularly active in that church (inactive membership does not count as supporting it). Logically, therefore, one could visit other churches during service and not be part of those churches. One can even do things with churches to support charity, again without belonging to those churches.
Of course, the Washtowel has the opposite viewpoint. While one must be 100% involved with washtowel activities, even passing 10,000 kilometers in front of a church constitutes belonging to it. Also, if you had a membership with 50 years since you were active and you forgot all about it (or the church went bust), you still have to terminate it deliberately. The washtowel even classifies doing something for charity with a church to be "in Babylon the Great".
Better, one should avoid Kingdumb Hells and A$$embly Hells to avoid Babylon the Great. You should avoid passing near those structures while there is activity going on, but only to avoid the threat that someone will come out and drag you back into the cancer. Avoiding groups of witlesses is also a good idea, again to avoid being hounded to join or rejoin the cancer.