A plumber would most likely have as much idea of how to vent an oil pump as you.
Yes you have been trying to vent from the wrong place and would...
Think he probably means over aired.
100 feet 15mm plus fittings could probably run a Bunsen burner ok!
Any of the sheds. Your local plumbers merchant, or just buy another
drain cock of the same type and change over the guts of it.
The valve without a wheel on it is the one to turn off.
Use a spanner or adjustable to turn off.
Open a downstairs hot tap to empty the pipe...
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