the dish detergeant helps to break the surfce tension of the water.
this improves the flow, reduces beading, and rings.
if you are doubtful, try the following:
take a small glas dish and add some water.
shake some black pepper on the surface.
it will likely float on the top.
rub your finger across the top of the liquid detergeant bottle,
or just rub a drop between your thumb & forefinger.
touch your finger to the water's surface.
i use artist's watercolors for my washes.
thinned w/ tap water, and w/ a drop of detergeant.
while i admit the oils may be better,
i like always having thinner on hand at the tap. :-)
and i never have to worry abt what the base coat paint type is.
water won't hurt it.
the vinegar i have not tried yet.
but i will on my next model!
anything for an edge.
if you don't have a test model to experiment on,
at least start on a hard to see spot on your model.
i started on the bottom of the hull just to be safe.
good luck,
ed.