Robert , I had a simil;ar situation . I used an NPT to Compression fitting , reamed it out so the tubing would pass thru , and used soft copper tubing . Straighten it as you feed it thru the fitting until you feel it bottom out then back it off a little . It's also nice to give the bottom end just a bit of bend so the water swirls at the bottom instead of causing turbulence that might douse a shower user with a cold surge . Mark the tubing so you can orient that bend ...
Only problem that I see is that if the existing tap is used, the volume of water will be restricted by the size of that tap vs. the inlet pipe. However, this doesn't sound like one of those repairs that is going to be expected to last a long time if one dip tube has already failed.
Tomsic
I had meant to quote the second link "Faulty dip tubes in water heaters made between 1993 and 1997 may cause hot water problems and clogging at faucets."
"If you have hot water problems (loss of water temperature and/or loss of water pressure at water delivery points) and your water heater was made between 1993 and 1997, you have a lot of company. During that time, nearly all the major water heater manufacturers were buying the same defective plastic dip tubes from the same manufacturer and installing them in their gas and electric units. Unfortunately, depending on your water chemistry, its pH and the temperature setting of the water heater, these tubes eventually break, crumble and/or dissolve into various size pieces.
The pieces clog strainers and filter screens on appliances and faucets, and the partial or complete absence of the dip tube severely harms water heater performance.
The role of the dip tube is to direct incoming cold replacement water to the bottom of the tank for heating. While it warms, the dense, cold water stays naturally segregated from the warmer, lighter water floating on top. The water for faucets and appliances comes from the hot layer on top. If the dip tube is missing, the cold incoming water mixes with the hot water at the top of the tank and you wind up feeding the house with tepid instead of hot water.
If you?re having hot water problems, first see if you have a water heater made during those bad dip tube years. Often, the first four numbers on the serial number are the month and year of manufacture. If the third and fourth numbers are 93, 94, 95, 96 or 97, it could be affected. If you have a bad unit, there are two options. First, replace the water heater and flush all the faucet screens and filters throughout the house. (If your water heater is more than 10 years old, it?s nearing the end of its life, so it?s probably worth replacing.) New water heaters have dip tubes that?ll last as long as the water heater.
Or second, replace the defective dip tube with a cross-linked polyethylene one and flush the debris out of the water heater and the screens and filters. You may have to flush the system more than once. "
or the third:
"That White Crud in Your Faucets May Be a Sign of a Decaying Hot Water Heater
My friends were certain that my hot water heater was plugged with calcium precipitate, and that I would need to purchase a new unit. Instead, the problem was a ten-dollar part that required about one-hour to replace. It's called a "Cold-Water dip-tube", and chances are good that you'll need to replace yours as well.
A cold-water dip-tube is a three-foot plastic pipe that routes cold water to the bottom of the hot-water heater. The cold water is heated, and then rises to the top of the tank, where it flows out to the house. Without that pipe, incoming cold water would immediately mix with outgoing hot water. Not very efficient.
In the mid 90's, many hot water heaters used defective plastic dip-tubes, and by 2010, they are breaking down into a fine plastic granulate. This is the first clue that your dip-tube is defective '" you'll be noticing a reduced flow through many of your hot-water faucets, caused by a build-up of these white granules. If you unscrew the screen from the end of the faucet, you can flush this plastic from the screen, and flow volume will be immediately restored '" but only for a week or so. After that, you'll again find a build-up of plastic bits. My friends and I mistook this for calcium carbonate particulates.
A shortage of hot water is another sign of a failing dip-tube. Since the water heater isn't working efficiently, the temptation is to turn up the water heater thermostat. But that doesn't solve the problem."
Instructions follow althought the part about unscrewing the diptube doesn't seem to apply to my WH from 20 years ago.
More than one person here has advised not to do that. Crud gets in the vavle they say and then the drain valve can't be closed. I've never tried.
Well, about two months ago, I rerouted the cold water input into the bottom of the tank via the drain hole. While hole was exposed, I could see (!!!) dip tube sitting on the diagonal at bottom of tank.
Since I did this, symptoms gone, No problems. Virtually endless hot water. It's *good* !
Hi, To the OP, Cold water dip tube is closer to the bottom any way. Isn't that enough? Find a diagram of hot water tank cut off side view, see for your self.
All water heaters are fed from the bottom - the pipe goes in the top for convenience, but routs the cold water to the bottom. Good water heaters have a "turbulator" at the bottom of the "dip tube" that causes the water to swirl in the bottom of the tank to prevent sediment build-up. You loose that when you feed tangentially from the drain fitting - but if the dip tube has fallen off you've lost that already anyway, and feeding tangentially at the bottom is better than dumping the cold water on top of the hot
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