Drastically increase your hot water capacity for less that $20!
While reading a thread on boon docking, I learned about a trick seasoned boon dockers use to conserve water. Basically, it's a re-circulation valve between the hot water line and the fresh tank, for the purpose of not wasting those several seconds of cold water that comes out of your tap before the hot water kicks in.
Using this extremely simple trick I have increased my hot water capacity to over 85 gallons, which is only limited there by the capacity of my fresh tank (75) and my hot water heater (10). I just finished a half hour long hot shower that only ended because I drained the tank.
What I did:
My water pump is located beneath the kitchen sink, as is the fill tube for my fresh tank. Yes, this setup makes this easier, but if yours is in a different spot it is still possible it just may require a little extra effort running the tubing. First I tee'd into the fill tube and then tee'd into the cold water line, connected the two with tubing and put a ball valve in the middle as an easy way to fill the fresh tank via the city water connection from inside the RV. If your rig already has this capability you may wish to skip that step. Then I tee'd into the hot water line and led it to the tee in the fill tube as well, again with a ball valve in the middle. Now, with your fresh tank filled, your city water OFF, and your pump ON, open the ball valve on the hot line dumping your hot water tank directly into the fresh tank. This takes the chill off the water in your fresh tank. After only two circulations I obtained a temperature of 90?F in my fresh tank. The "trick" behind it is that the warmer the water is going into your hot water tank as you empty it, the less energy and time it takes to heat that water to the optimum temperature, as well as the less it cools down the hot water already in your tank.
I just had my first long, hot shower in a long time in which I did not have to rinse off in cool or cold water, and even had time to shave and otherwise just enjoy the shower!
Do NOT over do it. 90? or so should be safe for any holding tank, but I am not responsible if you over do it and melt a hole in your fresh tank.