I have not been taught to do this. While I understand the risk of hypotension, I think there are other ways to deal with that than to clamp and deal with the issues of stagnant urine.
While a "typical" normal void might be about 400 or so, who hasn't had the experience of voiding & looking and being "impressed" with the volume -- "wow, I bet there's at least 600mL in there ..." :chuckle
What about pts. on Lasix who void 400-500, the same amount 20 minutes later, and again 20 minutes after that? In my experience, few of them are hypotensive.