Something like this?
private static TextureAtlasSprite getStillFluidSprite(FluidStack fluidStack) {
Fluid fluid = fluidStack.getFluid();
FluidAttributes attributes = fluid.getAttributes();
ResourceLocation fluidStill = attributes.getStillTexture(fluidStack);
return Minecraft.getInstance().getTextureGetter(PlayerContainer.LOCATION_BLOCKS_TEXTURE).apply(fluidStill);
}