From Longman Dictionary of Contemporary Englishunblockun‧block /ʌnˈblɒk $ -ˈblɑːk/ verb [transitive] if you unblock a pipe, you remove something that is blocking itunblock a toilet/drain/chimney etc→ See Verb table
Examples from the Corpus
unblock a toilet/drain/chimney etc• Watchdog featured her after she called out a plumber to her home to unblock a toilet. 