If you are using it straight out of the bottle, then yes, it will seem "sticky". It's just another paint colour (albeit a transparent one) so it has similar characteristics (ie. similar viscosity) to "normal" opaque Tamiya gloss paints and is usually used to "tint" transparent parts like car windows If you are using it as a wash, it will require thinning. Sorry, I can't suggest a thinning ratio for you as I haven't tried to use it as a wash.
For thinner, I would use Tamiya thinner rather than distilled water. One rather undesirable characteristic of Tamiya's transparent colours is that they have a nasty tendency to pool and bead due to surface tension, depending on the surface you are applying it to. It shouldn't be a problem over a "flat" surface, but you may find it beads up on gloss surfaces. Also, if you are using it as a wash, you may require a "barrier" layer if applying over an acrylic base.
Good lick ![Smile [:)]](/emoticons/icon_smile.gif)