The best replacement for inlet is bay.

The best alternatives to inlet are rated as following:
★★★★★  bay
★★★★★  outlet
★★★★  cove
★★★★  catch basin
★★  thoracic outlet
★★  fjord
★★  pelvic outlet
★  pawleys island

Your alternative for inlet is not listed? Suggest!
Speaking about inlet, one probably shouldn't forget about single ventricle.

Other search terms related to inlet and their ratings are:
★★★★★ single ventricle
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inlet
bay
outlet