Sweat rate and IMC training days 7-8

I know I sweat while biking and running but I've been curious if I sweat or lose fluids while swimming so I decided to start checking with my swim sessions. My YMCA has a really nice digital scale in the locker room so before and after my swims, I checked my weight. Holy moly, what an eye-opener. I know my maximum sweat rate on my bike or run is 4 pints per hour (1/2 gallon or 4 pounds) on hot summer days. It's less depending on exersion and outside temperture.
Now here's the eye-opener. When I swim in an 83 degree pool, I sweat (fluid loss, not peeing) an average of 2 pints per hour! (2 pounds). That's a whole quart of water every 2,500-3,000 yards.
If I extend that data to my ironman swim of 1:04.00 (IM Switzerland 2007), I'm at least a quart low going in to T1. Gee, I guess it's pretty dang important to start drinking as soon as I get on the bike to catch up on fluids and keep them up.
Here's a little namonic divice to help with how much water weighs.
"A pint is a pound the world 'round." 1 pint weighs 1 pound.

I've read some other methods of how to calculate your sweat rate by weighing yourself before and after a workout and then figure out how much fluids you took in during the work out and subtract that from your weigh-in and 6.02 times 10 to the 23rd power of E=MC squared....please!
Here's what I do. I really suck at math so I've learned to adapt an easier way.
I know about how many water bottles I need for any given work out.
Let's use my bike rides as an example. During a 120 minute ride, I'll go through almost two 20oz. bottles. Rather than doing that hard math. I fill up 2 bottles, get naked, and stand on the scale while holding the 2 bottles and note my weight.
After the ride, I take the 2 bottles (at least one is empty and one might have some liquid remaining) and get naked again and stand on the scale while holding the 2 bottles again and note my weight. The weight difference is the fluid loss.
4 pounds is 4 pints. 5 pounds is 5 pints etc.
Why get naked for the weigh-ins? I assume that if I weigh myself clothed before and after my workout, the after workout weight would include my sweat soaked clothing and throw off the weight of fluid loss because the fluid loss from my body is still clinging to my cloths.
Oh sure, it gets tricky if I refilled one bottle along the way or ate a PB&J sandwich but I just don't bother checking sweat rate on those days. I only check when I know all things are controlled.
Easy for me.

Thursday
60 min Body Flow (Tai Chi, Yoga, core work)
60 min Spinning class
40 min run:
10 min wu
20 min aerobic w/ 4x20 sec. fast w/ 40 sec. ez between.
10 min ez

Friday
Swim
WU 400 free, 100 Kick, 100 pull
5x50 backstroke @ 1:00
3 times:
3x50 drills @1:00
3x200 Kick as:
200 flutter @ 4:45
200, last 25 of ea. 100 dolphin K @4:45
200 k and s by 50's @ 4:05
Yeah, I'm one slow kicker.
600 pull @ 8:55:
1st 300 anchor catch then rotate hips
2nd 300 long and fluid strokes
4x50 @ 1 min. restrict breathing every 7 strokes
100 ez
2,800 total. 65 minutes.