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Discussion Starter · #1 ·
This may seem like a simple question but, you never know. Several years ago I replaced my tank water heater with a tankless, which is located in a utility closet on the third floor of my townhome. Each year I flush the unit with vinegar and then rinse with clean water. Currently, I’m carrying a 5 Gallon bucket of vinegar, then rinse water down the stairs to dump into a bathroom Sink. But, I’ve been wondering if I can just siphon it down the old tank drain To eliminate carrying dirty liquid over my hardwoods and carpet. I assume this drain is connected to the waste system.

Does anyone see an issue or, the fact that the drain has never had any liquid through it in 20+ years?
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Super Moderator
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I don't see any problem with that.

But before you do, don't assume anything, I would verify exactly where it drains to, (outside, dwv, sink) ect., and make sure it's not clogged before you go dumping 5 gallons of water down it. Just a suggestion.
 

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I agree, it looks like it was used for an emergency drain in case of a water heater tank failure or overflow. It looks like it was connected directly to the drain pan.

Sometimes those just get piped to the outside of the house somewhere, no trap required. If it connects to the your municipal dwv, it would need/require a trap so sewer gas doesn't come back through. Don't assume, verify. Just a suggestion.
 

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Naildriver
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I am sure it will work provided the pipe is clear and you can find where it emerges from the house. Just be aware, vinegar is acetic acid and will probably kill all the vegetation it touches initially, and cause weeds to flourish since they like acidic soil.
 

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retired framer
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If it is attached to the sewer it would have a trap and a trap primer connected to the cold water line.
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Vinegar, unless you let it sit in the "tankless" for a while isn't doing much.
How long do you keep the vinegar in the heater....an hour, longer?
Flushing won't do much, it's like a quick douche.....not really effective.
 

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Naildriver
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On a tankless you recirculate the vinegar via a pump and hoses. There's no place for it to "sit". It's like backwashing a pool filter. You run the vinegar backwards through the heat exchanger and back into a bucket for about 45 minutes or longer.
 

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Discussion Starter · #8 ·
To descale, the Rinnai maintenance instructions state to circulate 4 gallons of undiluted white vinegar ( no chemicals) through the unit for 45 minutes, which is what I do using a bucket and a sump. The liquid is always dirty when I finish. So, it must be doing something.
 
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