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I ride a Btwin MyBike 7s.
Yesterday morning I noticed (for the first time since purchase) that in my rear tire, the tire pressure has decreased to a flat. I thought it was a puncture, so I refilled the tire using a hand-pump and poured water over the tires expecting bubbles but didn't get any.
Then I took it for a ride, 20 kms and came back - nothing happened.
Then I came back in the evening to notice that the air pressure has decreased again, almost half. Then today morning it's a flat again.
Is it a puncture? I checked the tire's mouth valve, it's not leaking any air there. Should I get the tube out and check for a puncture?