Is unagi(eel) sauce for sushi supposed to be watery?!
Answers:
Maybe that unagi sauce is for "unagi and rice"?
I mean, in Japan, when we eat rice with unagi, we pour some sauce over. That sauce is thinner than the one you find on sushi.
The sauce you have is most likely rather sweet. If so, by reducing it down, you can make it thicker.
I think TLK's answer is right.
This below link may be of some help for you to know more about "Unagino Tare" or unagi sauce.
http://www.google.co.jp/search?q=%E3%81%…
What you purchased was "kabayaki sauce". You use that to marinade your eels. You also brush it on your eel when grilling.
That thicker sauce brushed onto unagi (BBQ freshwater eel) after it was grilled was actually teriyaki sauce.
There are different types of unagi sauce. Usually, having thicker sauce makes it easier for you to prepare, but if the taste is the same, then here shouldn't be any problems.
Unagi sauce should not be watery. It should have a nice thick consistancy, this makes for easier application and hold onto the food better.