Which preposition to use with bathtub

in Occurrences 2%

And finally, with a deep sigh of accomplishment, he filled one of the bathtubs in the adjoining roomfilled it to the slopping-over point with the luxurious hot water, and he splashed about in this, and reclined in it, gloriously, until the waiting ones threatened to pull him out.

of Occurrences 1%

So I got him off to bed, first pouring him a bathtub of warm water.

Which preposition to use with  bathtub