We used the technique Richard described to ground plastic containers.

There are a lot of other variables involved in static ignition. Besides quantity, is the liquid conductive, could the plastic containers become charged by plastic wrap or something else before filling?

More references, if interested:

NFPA 77 Table B.1 lists minimum ignition energies and B.2 lists conductive, semi-conductive and non-conductive liquids.

Britton, L. (1999). Avoiding static ignition hazards in chemical operations (CCPS concept book). New York: Center for Chemical Process Safety of the American Institute of Chemical Engineers.

Adapted from CCPS text - Plastic wrap is removed from a plastic container, this induced a static charge on the container. A conductive liquid, like acetone, is poured into the charged plastic container. The acetone takes on this charge. A metal funnel is inserted into the container. A spark goes from the charged acetone to the funnel. Or if the charged acetone is poured out a spark may also occur then. In either case the spark could ignite the flammable liquid.

http:​//www.srbrowne.com/booklet/page03.html

The use of nonconductive, plastic containers in potentially flammable locations may be an ignition hazard in plants. Static charge accumulations on such containers, caused by the transfer of poorly- =ADconductive liquids or solids, or by contact charging, cannot be dissi =ADpated by the bonding/grounding system.

Contact ("triboelectric") charging of a nonconductive container in a low humidity environment creates a spark ignition hazard by inducing charges in the liquid in the container. These induced charges may cause sparking, e.g., when the liquid is poured into a grounded safety can. Surprisingly, this hazard of charge induction is greatest when the liquid is "conductive".

https:​//www.paint.org/wp-content/uploads/2015/09/ACA_cc_static_guide.pdf

Removal of plastic bottles from plastic bags may cause high contact charging. Electric field intensities greater than 5 kV/cm (12.5 kV/inch) at the surface of the bottle or liner should be neutralized before a conductive flammable liquid is put into the bottle (21). It is also important to avoid charging a plastic bottle that contains even a small quantity of a conductive, flammable liquid.