While replacing the washer in a bathroom tap/faucet, I've accidentally loosened the fitting (e.g. the tap now turns when I turn the tap "handle").
Here is a photo of the underside of the sink, with the specific part I need to get tightened circled.
There's very little space - I can grip it with my fingers but can't apply enough force to get it properly tightened. It's plastic and I've tried pliers but couldn't open them sufficiently wide enough to grip, and I've tried an adjustable wrench but when I've angled it to actually grip the fitting there's no room to turn the wrench handle.
Is there some tool that will let me tighten this without actually taking the sink off the wall?