Probably one of these, McAlpine doesn’t appear to state it’s not permissible underground:
McAlpine DC1-BL Drain Connector Black 110mm - https://www.NoLinkingToThis/p/mcalpine-dc1-bl-drain-connector-black-110mm/4255V?tc=TA8&ds_kid=92700055281954505&ds_rl=1249404&gclid=Cj0KCQjwp86EBhD7ARIsAFkgakimgaxhTGG88BeGgZ9r-n_AJ-w9ssg64H44HND6JZfvUCfR2utqhIMaAgQmEALw_wcB&gclsrc=aw.ds and a short length of soil pipe with a slip coupling.