It only seems absurd when you have the typical misconception that it's waste product. And if it were, I would certainly agree! But it's not.
Not only is it not waste, but it is also very sterile. Even mainstream medicine knows this (although that doesn't mean much). The only element of urine that is considered "toxic" (assuming you aren't passing highly toxic things into your system in the first place) is urea. This is toxic if present in large amounts in the blood, but it is not a concern with UT (it might be a concern when dealing with extracted/concentrated urea though!). In normal UT practice, the amount of urea introduced into the body is very small (only about 2-3% of urine consists of urea), in addition to the fact that it's not being introduced directly into the blood. This very small amount of urea is actually considered beneficial as it helps regulate natural flushing of the colon when it's needed. Urea also has other beneficial properties, especially with regards to things like Cancer. I repeat: Its toxicity is mainly in large quantities, just as salt, sugar, or even the potassium in a banana! In normal use it is not harmful at all.
All other elements of urine are the direct "leftovers" or "extract" from the blood -- not because those elements are "bad", but because the blood requires a very specific balance of things. The kidneys perform filtration in order to BALANCE levels in the blood. All these excess elements are generally passed into the bladder, along with water and urea (of course, the "efficiency" of this process -- how will it balances the blood -- depends on what condition your kidneys are in, just as with any other bodily organ).
Urine is then the "leftovers" of the foods you eat, basically, but without the physical and cellular waste (which have already been filtered out by the intestines, liver (for the cellular), and colon).
You might then ask, "Still, if the blood didn't 'need' it, why re-consume it?"
The demand for certain elements in the blood is CONSTANTLY changing due to many, many factors. For example: The foods we eat throughout the day, stress levels, physical activity, and even emotions or mood, just to name a few. What the blood didn't have a "demand" for an hour ago, it may have a use for now. Recycling the urine makes much more efficient use of the foods you eat, providing a greater "availability" of many useful elements for the blood to use as it needs. It is vey easy on the body since it has already been filtered of waste material, and the water is in a more structured state which is easier for the liver and kidneys to handle.
The liver sees this recycled urine and says: "Hey, welcome back old friend. I've already dealt with you so I know you're pretty clean, but I'll do a quick once-over just to make sure. Say, think I could borrow a little bit of X-element to help give my 'workers' a little extra boost and rejuvination? The kidneys around the block won't notice, I promise. Whew, thanks, I sure am glad you came. Things around here are pretty stressful... at least with you I know I can take a brea-- UH OH, MORE WASTE COMING IN, BREAK'S OVER."
These "leftovers" in the urine are not "dead cells", but instead very vital and nutritious elements directly from the foods you eat and your own blood (which are basically synonymous -- you ARE what you eat!). Of course, it's important to "recycle" the urine fairly soon after it's released. After about 15-20 minutes of being out of the body, certain aspects of it begin to break down, making it unsuitable (from what I've learned anyway) for internal use -- however, due to whatever conversions take place as it ages, it becomes very beneficial for external use!
Not only is urine a "vital substance", rich in many different elements, but on a more esoteric level your own "energy", or "energetic fingerprint/blueprint", is also present. I won't get into what this means, but it's something to ponder over.