Section 22. If an ordinance or by-law provides that any drain or sewer laid in any land or way, public or private, which is opened or proposed to be opened for public travel and accommodation shall be a main drain or common sewer, and such drain or sewer is laid in a private way or land at the expense of the owner thereof, his land shall not be assessed for such drain or sewer, except for the cost of connecting it with common drains or sewers already established.