Answer: caulks

AnswerCrossword Clue
CAULKS

Makes watertight

CAULKS

Fixes leaky boat seams

CAULKS

Prevents leakage, perhaps

CAULKS
Makes airtight
CAULKS
Seals cracks
CAULKSMakes watertight, in a way
CAULKSSeals around a bathtub
CAULKSFills in the gaps?